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. 



