Section IV, 1880. [ 1^3 ] Teans. Roy. Soc. Canada. 
 
 X.—Somc Remarl-s on the Cla^'sification of the Trilobites, as influenced Inj Strati- 
 (jraphkid Relation.s : toith Outline of a New Grouping of these Forms. By 
 E. J. Chapman, Ph.D., LL.D., Professor in the University of Toronto. 
 
 (Kead May 8, 1889.) 
 
 (1.) It may be takon as an undoubted fact that pal:voutologioal classification has 
 been very greatly iuiiuenced of late years by stratigraphical considerations. This is 
 seen not only in the current subdivisions of the Trilobites, but in those also of the 
 Ammonites and other extensive groups. These stratigraphical classifications have the 
 advantage of being readily effected. They save trouble, by requiring little or no thought 
 for their construction, and they are of course useful to the geologist as paloeontological 
 lists : but there their value ceases. Structural afliuities become by this plan more or less 
 unrecognized ; and forms with but few characters in common, if occurring at the same 
 geological horizon, are thus often forced into false relationship, rendering even moderately 
 rigid definitions of families ai:d other groups practically impossible. 
 
 (2.) It might be thought, in opposition to this view, that contemporary forms of a 
 given order or family must be more nearly related to each other than to forms of the 
 same order or family occurring at earlier or later periods. But this conception is cer- 
 tainly in the main erroneous. Forms of the same geological horizon should naturally otfer 
 fewer points of generic agreement than forms of dilferent horizons. The latter may be 
 connected by more or less direct evolution : whereas forms of the same horizon '-an only 
 be related generically, if at, all, through some remote ancestral type, from which, also, 
 other distinct orders and classes may have sprung. In one case, there may be direct 
 relationship : in the other, the conueition can be little more than indirect. 
 
 (3.) An impression prevailed widely at one time, and perhaps still prevails, that the 
 so-called " Primordial Trilobites " are distinguished from the Trilobites of higher horizons 
 by a combination of iharacters peculiar to themselves, by which a marked " primordial 
 aspect" is imparted to them. These characters, as commonly formulated, comprise : — A 
 large, typically horned or spiny head-shield, wilh numerous body segments and a A'ery 
 small pygidium. This definition fails, of course, completely in the case of the eminently 
 Cambrian family, the Agnostida;. But setting aside these still somewhat problematical 
 forms, and looking only to the typical Trilobites, it is foxmd to be equally inapplicable ui 
 many other cases. Whilst, for example, it holds good in Paradoxides, Olenus, Eurycare, 
 and some few other Caml^rian genera, we find the same combination of characters — the 
 large and horned head-shield, the long thorax, the small pygidium — present also in 
 Harpes, an essentially Upper Silurian and Devonian genus, unknown in Cambrian strata. 
 The imaginary primordial aspect is suiiiciently well marked in the Cambrian Olenus ; 
 but in the Silurian and Devonian Arethusina or Aulacopleura we see a combination of 
 characters very similar to those of Olenus, among whi<'h may be specially cited the 
 comparatively short glabella, spiny head-shield, open facial suture, small eyes connected 
 
 Sec. IV, 1889. 15. 
 
114 
 
 K. J. CHAPMAN 
 
 by a ridge or baud with the glabelhi, narrow body-axis with numerous or comparatively 
 numerous segments, and small, short pygidium. Again in the Cambrian Dikeloeephalus, 
 and in Cteuopyge (Linuarsson), the pygidium is very large — thus presenting a marked 
 departure from the so-called primordial type. Other examples might be cited to prove, 
 (1) that these imaginary primordial characteristics are present in various post-primordial 
 genera, and (2) that they are not always present in primordial or Cambrian tyi^es. 
 
 (4.) Nothing. p<^rhaps, shows more forcibly the arbitrary, unnatural character of 
 stratigraiihical groupings, than the collocation in recent classiiications of Neseuretus, 
 Hicks, side by side with Paradoxides in the family of th<' Olenidte. In all its leading 
 characters, Neseiiret as is simply a Cambrian Calymenc, probably the ancestral source of 
 the latter type ; l)ut in the classifications referred to, these genera are placed in ditlerent 
 families and widely apart. To show these points in all their distinctness, viz., the close 
 agreement of Neseuretus with Calymeue, and its remote relations to Paradoxides, a com- 
 parative view of their more characteristic structures is given in the following table ; — 
 
 
 NESEVKBm-S. 
 
 Calymbse. 
 
 PARilW-XIDEi. 
 
 Glabella 
 
 Contracted anteriorly, 3 later- 
 al furrows- 
 
 Contracted anteriorly, 3 later- 
 al furrows. 
 
 Expanded anteriorly. Trans- 
 verse and lateral furrows. 
 
 Tliorax 
 
 13 segments 
 
 13 segments 
 
 10 to 20 segments. 
 
 Pygidium 
 
 Comparatively wide, witli fur- 
 rowed sides, an<l 8 to 10 
 rings in its axis. 
 
 Of moderate widtli, with fur- 
 rowed sides and (> t(j 11 
 rings in its axis. 
 
 Very small and narrow, with 
 rarely more than 2 or 3 
 rings in its axis, the sides 
 forming merely a smooth 
 border. 
 
 In these recent clajsiiicatious, also, we find Dikelocephalus arranged under the 
 Olenida*, whilst Arethusina and Harpides, which agree very strikingly with Olenus in 
 their more salient characters, are placed far apart from the latter under the Proetidte, 
 evidently upon purely stratigraphical grounds. The structural relations oi these genera 
 are brieflv indicated in the annexed tabular view : — 
 
 
 DiKEi.ocEPiuLue. O1.ENCS. AKErriiusiNA. 
 
 Glahdla 
 
 Facial stttwes ■ 
 
 Comparatively large, Comparatively small. Quite small. 
 
 Forming a point above the Open anteriorly. Open anteriorly, 
 glabella 
 
 Eyes 
 
 Large. Unconnected with tho 
 glabella. 
 
 Comparatively small. Con- 
 nected by a hand with the ' 
 glabella. 
 
 Comparatively small. Con- 
 nected by a (Kind with the 
 glabella. 
 
 Body-axis. •••• 
 
 Comparatively broad 
 
 Narrow. 
 
 Narrow. 
 
 Pygidixem 
 
 Very large, with comparative- 
 ly short axis. 
 
 1 
 Small, but with extended Small, but with extended 
 axis. axis- 
 
 i 
 
ON TEILOBTTES. 115 
 
 (•").) As the Trilobiles have no known Post-Pakuozoic representatives, and are prac- 
 lioally confined to strata representing the earlier and middle periods of the Pakeozoic Age, 
 broad dislimtions, surh as those which separate the Pakeozoic Criuoids and Eehinida from 
 Mesozoic and higher forms oi' these orders, cannot obviously be looked for in any 
 classification. Added to this disadvantage, there are other drawbacks which beset at 
 present, and render dilFieult, the systematic grouping of the Trilohites. lirielly stated, 
 these comprise, first of all, the very lax manner in which fragmentary examples have been 
 referred to known types, or placed, as new genera, in families with which they have but 
 few points of resemblance. Definitions, applicable enough in the first instancfe, become 
 thus, after a time, of almost impossible application — the original definition being so 
 extended as to iiicludt> forms of very dissimilar structure. Mathematically rigid defini- 
 tions in the grouping of organic forms cannot, of course, be strictly enforced without, at 
 least, greatly multiplying our classification groups ; but better an undue multiplication 
 of orders and families, than this license of indefiniteness that now so habitually prevails. 
 Another source of difficulty lies in the remarkable dissimilarity of aspect which exists in 
 tho .•■)se of many species commonly referred to one and the same genus, as seen in 
 Asaphus, Proetus, Cheirurus and other forms. This has led to the creation of numerous 
 sub-genera, by which, how^ever, the diihculty is in no way lessened — family definitions 
 still remaining vague and diffuse. 
 
 (G.) In the classification shown, as regards its leading features, in the annexed 
 synopsis, the Trilobites, considered as an order of Crustacea, are arranged under four sub- 
 orders, or primary groups, founded on general structure and configuration, with subordi- 
 nate sections based, as far as possible, on some striking or typical character. This latter, 
 however, is to be taken in connection with the general characters of the sub-order to 
 which the section may refer. The names attached to these sections refer necessarily to 
 single characters, and they are thus to be regarded as names only, not as defmit.'ons. It 
 is thought, however, that they may serve to bring rapidly before the mind's eye the more 
 salient or special features of the types to which they refer. In the collocation of the 
 families, an attempt is made to place them in as connected a sequence as possible, so that 
 each family shall present relations to the family which tbllov>'s it, whether placed in 
 the same section or under contiguous sections ; but in a linear system of arrang(>ment, 
 and especially where the objects to be classified are not very numerous, it is not possible 
 to avoid occasional breaks in the continuity of the series. 
 
 In offering this new classification, I am not sanguine enough to expect that it will 
 meet with general acceptance. In its subdivision of genera, and the recognition of these 
 subdivisions in one or two cases as the types of new families, and in its disregard of 
 stratlgraphical considerations, it will necessarily rullle existing prejudices. Hut it may 
 tend to bring under more immediate notice the indefinite and hence unsatisfactory 
 character of our commonly received subdivisions, and so lead eventually to a more 
 successful groxiping of these ancient forms. 
 
116 E. J. CHAPMAN 
 
 Order TKII.OBITA. 
 
 Sub-Ordcr I.— PUSILLIFORMES.— Small, aberrant trilobites, with typically two thoiaoic segments, 
 and head-sliield and pygidinm of nea, '3' ecjjiial size. 
 
 Fam. 1. Agnostidw. — Typical <^enus, Agnostus, Cambrian, Lower Silurian. 
 
 SnlvOrder IT.— LATIFOEiLFS :— More or loss broad, often Iar<re, trilobitcs, with head-shield, thorax 
 and pyj^idium of nearly equal dimensions. Bod^'-seifments t3-])ically 8 to 10 in number. 
 Surface of shell commonly marked with wavy marginal lines. 
 
 § 1. Levati. — Broad-formed or oval trilobites, with essontially smooth shell, and inconspicuous or 
 feebly elevated glabella. 
 
 Fam. 2. lllatiicLv. — Pleura; unfurrowcd. Pygidium with smooth sides and smooth or feebly fiii-i-ow- 
 ed axis. T^-p. gen. : i/Zfrnus, Up. Cam., Sil. ; Bumastus,^\\.; i\7ta/5, Lr. Sil. ; S^'y/nfl, Lr. Sil. 
 
 Fam. 3. Asaphida: — Pleura) fun-owed. Pygidium with smooth sides and smooth or feebly furrowed 
 axis. Typ. (Jen.: Ilhvtmrus, Cam.; Niohe, Lt. Sil. ; AsapJan', Lr. Sil. ; Psilocephalus, Cam.; 
 Barrandia, Lr. Sil. ; Bnthyiinllus, Lr. Sil.; Batlujurus, Cam., Lr. Sil.; Megalaspis, Li-. Sil. 
 
 Note. — The two families of this section, although widely separated in the classification of 
 Barrande, arc very closely allied, and are commonly united in more recent systems, principally from 
 the fact that certain genera — lllsenurus, Niobe and Stygina, more especially — appear to form an 
 intermediate or transition group. But the tj-pical ''epresentatives of each famil}' are clearly charac- 
 terised, and connecting points of this kind are ab. ndantly traceable in the case of other families 
 universally regarded as distinct. In the present classification, indeed, the collujation of the families 
 is based, as far as this can be carried out, on the existence of these connecting or transitionary forms. 
 
 As regards Family 3, I have separated from the Asajjliidfc proper the forms with horned head- 
 shield and strongly furrowed ]iygidiuni, and have placed these in a distinct family under the generic 
 name of Basilicus, already applied to them, as a sub-genus of Asaphus, by Salter. This is warranted 
 by the very marked contrast presented by these strongly furrowed, lobate and conspicuously horned 
 forms, to the smooth IllffinidiC and Asaphida-. The horned genus, Megalaspis, forms the connecting 
 link. 
 
 § 2. SuLCATi. — Broad-formed or oval trilobites with horned head-angles, pointed pleurir, and large, 
 strongly-furrowed pygidium. 
 
 Fam. 4. Basilicidce — Glabella with short side-furrows, cr smooth. Typ. gen. : Basilicus (j= Asaphva 
 in part), Lr. Sil.; Oxi/gia, Lr. Sil.; Jfomalotopeon. Lr. Sil. 
 
 Fam. 5. Dikeloceplialidm. — Glabella strongly- developed, ivith transverse or side furrows. Number 
 of body-segments unknown. Typ. gen. : Dikelocephalus, Cam.; D or ijptjge, Cam. 
 
 Note. — Dikelocephalus, as a Cambrian type, is commonly placed with Parodoxides and other 
 Cambrian forms under the family of the OlenidiB. But fiom these it is distinctly separated by its 
 large pygidium. This latter character, together wilh its horned head-shield and the meeting of its 
 facial sutures in a spado like point above the glabella, connects it far more closely with the horned 
 and furrowed Asaphidic or Basilicida-, in many of which, as well as in many species of the Asaphidio 
 proper, the course of the sutural outline is the same. '^'. '"eater number of Iwdy-segments may 
 
ON TRILORITHS. 117 
 
 prove to bo a divergent character, but tlie actual number of llie.se is at present uncertain, and in the 
 closely related Dorypyge the thorax is entirely unknown. 
 
 4^ .".. Palmati. — Broad-formed triiobites, wilh lari^e, .short-axcd, radiatei3'-furro\ve(l pygidium. 
 
 Fani. ('). Lichasichv. — Pleuia: fmrowcd. T'ygiciium with short, broail axi.s and deeply indented 
 margin. Typ. gen. : Lichas, Sil. 
 
 Fam. 7. Bronteido'. — Pieurai wiih slightly raised surface-band. Pygidium with veiy short axis and 
 entire margin. Typ. gen. : BTOH/ci/s, Lr. Sil, Dev. 
 
 § 4. CoLUM.VATi. — ^Trilohites of more or less oval form, with largo ]iygidium, the axis of which is 
 l3-pically long, promiricnt and many-segmented. 
 
 Fam. 8. PAaefon/(/a'.—ti label la short, conical. Body-axis comparatively narrow. Pygidium in 
 some cases with digitulcd outline. T^'p. gen.: Phaeton, Sil., Dev. ; Dcchnnella, Dev. ; 
 Brachtjmetopus, Carb. 
 
 Fam. 0. Proctidtv. — Glabella lai'ge. smooth or furrowed. Body-axis comparatively broad. Axis of 
 iiygidiura typically wilh 10 or moie pseudo-segments. Typ. gen.: Proetus. Sil., Dev.; 
 Phillipsia, Dev., Carb. ; Griffiihides, Carb. 
 
 Note. — The famil}' of the Proetida', as commonly recognized, includes under the genera Proetus 
 and Phillipsia forms of marked dissimilarity jf a.'<pect, so far, at least, as regards the glabella and to 
 some extent the i-elative width of the body-axis. Whilst in Pioetus proper the glabella is very large, 
 reaching quite, or very nearly, to the anterior margin of the headshield, in the forms referred to the 
 sub-genus Phaeton (= Proe'usstrkitus, Barr.) it is remarkably short and small. The digitated margin 
 of the pygidium, sometimes referred to as a sub-generic distinction, is a character of quite subordinate 
 value. In Deehenelhi and in Brachymotopus, commonly placed under Phillipsia, there is a similar 
 departure, as regards the glabella, from the typical generic form '. I have, therefore, separated these 
 tj'pes with short glabella from the genera with which they are commonly associated, and have placed 
 them in a distinct family. 
 
 Sub-Order III. — CONIFRONTES.— Triiobites of more or less elongated form, tapering downwards. 
 Body-axis of 13 or more segments, not distinctly separated fi'om the pseudo-segments of the 
 axis of the pygidium. The latter, typically, of moderate size, or small. Glabella : -coniform, 
 contracted (or not expanded) anteriorly. 
 
 § 1. LoNGicoNi. — Glabella comparatively lai-ge, extending to, or nearly to, the anterior margin of 
 the head-shield. Facial sutures terminating at the genal angles. 
 
 Fam. 10. Somalonotidcc. — Longitudinal furrows feebly indicated. Glabella: flat, typically unfiirrow- 
 ed. Typ. Gen.: Homalonotus, Sil., Dev.; Burmeisteria {= H. arnirtfus and other spinose 
 forms), Dev. 
 
 Fam. 11. Cali/menidd'. — Thorax, pygidium and glabella, strongly lobed. The glabella tapering 
 anteriorly. Typ. gen.: Cal y mene, Si\.; JVeseuret us, Cam. 
 
 Fam. 12. Triarthrida'. — Glabella of nearly uniform width, with side furrows. Body segments 14 to 
 15 in number. Typ. gen. : Triarthrus, Lr. Sil. 
 
 Note. — Homalonotus, commonly placed under the Calymenida>, is hero separated on account of 
 
 ' Ko doubt a series of intermediate varieties might bo found in which tlio distinction becomes gradually 
 lessened or obscured ; but connecting series of tliis kind may be traced more or les.s everywhere, and if rigidly 
 followed out woukl render generic distinctions practically impossible. 
 
118 E. J. CHAPMAN 
 
 its very distinct aspect, fn some of its forms it looks almost like u transition type between the 
 Calymenidii' and the Asaphidie. Triarthrus, which nuich leseniblcs Calymeno in its facial suture, 
 pleura) and pygidiiini, forms the connecting link between this seelion and the Conoecphulida>. 
 
 § 2. CuRTicoNi. — Glabella typically short, smooth or lightly fui-rowed. JJody-rings 12 to 17 in 
 number, typically over I'.i. Pygidium ^mall or comjiarativcly small, with typically 2 or 3 
 (more rarely 6 to 8) rings in its axis. 
 
 Fam. 13. Conocephalichc. — Kycs present. Typ. gen. : Elllpsoce})halus (?), Cam. ; Ciji>has}iis, Sil., Pev.; 
 Amjetina, Cam. ; Cunocephalites, Cam., Lr. Sil. ; Ayratdus (= Arwndluti), Cam. ; Liostracus, 
 Cam. ; Piijcluiparia, Cam. ; Solenopkura, Cam. ; Sao, Cam. 
 
 Kam. 14. Conocoryphida;. — Eyeless forms of Comcephaltdw. Typ. gen. ; Conocoryplie, Cam. ; Cttno- 
 cephalus, Cam. 
 
 Note. — The genus Ellipsocophalus, as regards the character of its glabella, is a somewhat 
 aberrant type; but in its genei-al stiucture and aspect it is closely related to the Conocephalidie and 
 cannot very well be placed in any other family. The separation of the eyele-is forms, typilicd by 
 Conocoryphe, is a convenient, if not strictly necessary, subdivision. Cyphaspis connects the Cono- 
 cephalidie with Arethusina. 
 
 s; 3. ViTTATi. — Eyes connected ii}' a narrow band with the glabella. The latter sliort and small. 
 Bt)dy-segments numerous, with nai-row axis. Pygidium, typically, very t-mall. 
 
 Fam. 15. Olen'dtr. — Bod}--segments 12 to 15 or Ki in number. IL .ad-shield straight nv flattened 
 along its anterior margin, and prolonged posteriorly into spines or horns. 'I"yp. gen. : 
 Olenus, Cam. : Eurycare, Cam. 
 
 Fam. Hi. Arethminida;. — Body-segments 22 in adult forms. Head-Shield semicircular, terminating 
 in points or spines. T^'p. gen. : Arethii>ina (= Aitldcopleura), Sil., I>ev. ; Ilarpidts, Cam., 
 Lr. Sil. 
 
 Fam. n. — Harpesidii'. — Head-shield very large and horned, with bro.id, finely punctured border. 
 Typ. gen. : ILirpes, Up. Sil., Dev. ; Ifirpina, Lr. Sil. 
 
 Note. — The section in which these families are placed is named after one of their more striking 
 cbaracterf, the band or fillet which connects the ej-cs with the sides of the glabella; but they have 
 also other points of agreement, as seen more especially in tlieir numerous bodi'-segments, their 
 narrow axis and small pygidium. Thrf)Ugh Harpides, the Harpesida' ]iropor are connected botii with 
 Arethusina and with Olenus. 
 
 Sub-Order IV. — FEONTONES. — Trilobites with large or stiongl^- pronounced glal>ella, widening as 
 a rule anteriorly. Pygidium very small or of moderate si/.e, the many-i'inged body-axis 
 extending quite or nearly to its extremity. 
 
 S 1. AsNULATi. — Many-ringed, comparatively elongated forms, with pygidium obscurely separated 
 from the thorax. Body-segments typically 1 1 in number. Facial sutures terminating at the 
 sides of the head-shield. 
 
 Fam. 18. Plwcopsida: — Pleurai furrowed. Eyes coarsely fticetted. Pygidium rounded or spinose. 
 Typ. gen. : Phacops, Up. Sil., I)ov. ; Dalmanites, Sil. ; Odontocephalus, Dev. 
 
 Fam. lit. Encrinuridii'. — PIcuito with raised band. Pygidium long, narrow, with mauy-ringed axis. 
 Typ. gen. : £ncrmurus, Sil.; Cybele, Jjv.Bil.; Cromus, Up. Sil. ; Amphion,l.v.BW. 
 
ON TBILOBITES. 119 
 
 Fam. 2(». ( 'hciruridn: — Pleura' with raised band. EycH finely facetted. Pygidinin hi^rncd, spino.so 
 III diii;ituled. Typ. ^ijcn. : '"'Af/ri/ri/s, Up. Cam., Dev. ; Pi ioplwn, V\t. S'i\.; Sjt/ia;rexochus,iii\.; 
 St(iur..cqiluiliis, Sil. ; Flacojuiria, Lr. Sil. 
 
 NoTK. — The taniilies of lliis section arc moi'c m- loss closely connecte<l by the pocnliai- course of 
 the lacial .-futures, alike in all, and by thcii' typically eleven body-sc/^mentrf. The Knciinurida' and 
 Cliciruridte, are connected by their " bourrclcttcd " pleurae ; and this same condition — as well as their 
 t<pino>e character generally — connects the Chciruridse with the Acidasj)idn3 of tho next section. 
 
 45 2. Ak-mati. — Hssentially broad-headed, spinoso forms, with pointed or spiny pleuijc, and small to 
 very small (commonly spine-bearing or digitated) pygidium. Body-scgmeids 1) to 20. 
 
 Fam. 21. Acidaspidw. — Head, pleursc and pygidium, all spine-bearing. Body-segments 9 to 10. 
 Pleura; witli " bourrelet." Typ. gen. : Acidasjies, Sil., Dev. 
 
 Fam 22. Faradoxidd'. — Head-shield ver}- largo and bruad, with horned angles and largo, anteriorly 
 expanded glabella. Body-segments 12 to 20 ; pleurte, furrowed, terminating in spines; Jiygi- 
 dium very small. Typ. gen. : Paradoxides, Cam. ; Hydrocephalus, Cam. : Telephus (?) Lr. Sil. 
 
 § 3. tlLOBOSi. — Glabella large and prominent, oval or globular, and unfurrowed. Thorax short, 
 with 5 to G segments. 
 
 Fam. 23. Trinudeida: — Head-shield very largo, terminating in horns, and surrounded by a broad, 
 perforated border. Eyes commonly absent. Typ. gen. : Trinucleus, Lr. Sil. ; Dionide, Lr. Sil. ; 
 Microdiscus {?), Cam. 
 
 Fam. 24. Ampyxid<c.—Ecad-sh'\G\d without perforated border. Glabella extended anteriorly into a 
 stiong spine. Eyes absent. Typ. gen. : Ampyx, Hi\.; Endymirma {f^iTJp. Cam. 
 
 Fam 25. jKijUnidw. — Glabella very large and globular, extended anteriorly, in some Bpccies, into a 
 stout spine. P'yes abnormally developed. Typ. gen.: uE(jUna,'Lv.^i\. 
 
 Note. — This latter family forms a connecting link between the (Jlobosi and the Oculosi. It 
 should, perhaps, be placed under the last-named section ; but it would apiiear to bo very closely allied 
 to tho Ampyxidic (notwithstanding Jie absence of eyes in that family) by its 5-0 body-segments, its 
 triangular pygidium, and its enormously developed iilabeila, which in some of its forms (e.g., ^E. 
 armaia, Bair.), extends forward into a distinct point or spine, much as in Ampyx. Whilst Barrandc 
 makes ^^glina the typo of a distinct family, Zittel places it under tho Asaphidic. 
 
 § 4. Oculosi. — Eyes enormously developed. Head-shield with horned angles. Pygidium very- 
 small, with 2-3 rings in its axis. 
 
 Fam. 26. ^o/temiVi^uZtr.— Body- segments 5 in number. Typ. gen. : Bohemilla, Lr. Sil. 
 
 Fam. 27. i?emo/>Ze«r('c/<i-.— Body-segments 11 to 13 in number. Typ. gen. : Eemopleurides, Lr. Sil., 
 Caphjjra, Lr. Sil. 
 
120 E. J. CHAPMAN ON TRILOBITES. 
 
 Summary. 
 
 Retrospective view of the Sub-Orders, Sections aud Families of the preceding classi- 
 fication. 
 
 Ori>er TRII.OBITA. 
 
 Sul)-Or(ler I.— I'USl IJJl-ORMKS. 
 Fain. 1, Agnostidffi. 
 
 Sub-Ordor II.— LATIFORMES. 
 
 § 1. Lkvati. 
 
 Fain. 2, Ill.ionidit!. 
 F\tm. 3, Asaphidte. 
 
 § 2. SUUATI. 
 
 Fam. 4, Basilicidio. 
 Fum. 5, Dikeloiephalidti;. 
 
 § ?,. 1'ai,m.\ii. 
 
 Fum. 6, Licliasidic. 
 Fum. 7, Bronteidic. 
 
 § 4 Col.l'MNATI. 
 
 Fam. 8, Phaetouidic. 
 Fam. 9, Proetidtc. 
 
 Sub-Order III.— CONIFKONTES. 
 
 § 1. LOXdlCX/NI. 
 
 Fam. 10, HomalonotidiO. 
 Fum. 11, Calymenidpc. 
 Fam. 12, Triartbrida?. 
 
 § 2. Cl'kticoni. 
 
 Fam. 13, Conooepbalidtc. 
 Fam. 14, Conocoryphidfc. 
 
 § 3. VlTTATI. 
 
 Fam. 15 Olonidio. 
 Fum. 16, Aretluisinidio. 
 Fam. 17, Harpesidio. 
 
 Sub-Order IV.— FKONTONES. 
 
 § 1. Annilati. 
 
 Fam. 18, Pbacopsid;e 
 tarn. 19, Eiicriuuridtc. 
 Fam. 20, Cbeiruridaj. 
 
 § 2. AliMATI. 
 
 Fam. 21, Acidaspidrc. 
 Fam. 22, Paradoxidse. 
 
 § 3. Globosi. 
 
 Fam. 23, Trinucleidse. 
 Fam. 24, Ampyxidic. 
 Ihm. 25, ^glinidie. 
 
 § 4. OCULOSI. 
 
 Fam. 26, Boliemillida?. 
 Fam. 27, Remopleurida?.