118 E. J. CHAPMAN 



its very distinct aspect. In some of its forms it looks almost like a transition type between the 

 Calymenidte and the Asaphidse. Triaithrus, which much resembles Calymene in its facial suture, 

 pleurœ and pygidiiim, forms the connecting link between this section and tlio Conoccphalidaj. 



§ 2. CuRTicONi. — CxlabcUa typically short, smooth ov lightly furrowed. Body-rings 12 to 1*7 in 

 number, typically over 13. Pygidium small or com^jarativcly small, with typically 2 or 3 

 (more rarely G to 8) rings in its axis. 



Fam. 13. Conocephalidœ. — Eyes present. Typ. gen. : EUlpsocephalus (?), Cam. ; Cyphaspis, Sil., Dev.; 

 Angelina, Cam. ; Conocephalttes, Cam., Lr. Sil. ; Agraulos (= Arionellus), Cam. ; Liostnicus, 

 Cam. ; Ptychoparia, Cam. ; Solenopleura, Cam. ; Sao, Cam. 



Fam. 14. Conocoryphidœ. — Eyeless forms of Conocephalidœ. Typ. gen. ; Conocorypjhe, Cam. ; Cteno- 

 cephalus, Cam. 



Note. — The genus Ellipsoeephalus, as regards the character of its glabella, is a somewhat 

 aberrant type ; but in its general sti ucture and aspect it is closely related to the Conocephalidœ and 

 cannot very well be placed in any other family. The separation of the eyeless forms, typified by 

 Conocoryphe, is a convenient, if not strictly necessary, subdivision. Cyjihaspis connects the Cono- 

 cej)halida3 with Arethusina. 



§ 3. ViTTATi. — Ej-es connected by a narrow band with the glabella. The latter short and small. 

 Body-segments numerous, with naiTOW axis. Pygidium, typically, very small. 



Fam. 15. Olewda'. — Body-segments 12 to 15 or 10 in number. Head-shield straight or flattened 

 along its anterior margin, and prolonged j^osteriorly into spines or horns. Typ. gen. : 

 Olenus, Cam. : Eurycare, Cam. 



Fam. 10. Arethuiinida'. — Bod^'-scgments 22 in adult forms. Head-shield semicircular, terminating 

 in points or spines. Typ. gen. : Arethusina (== Aulacopleura), Sil., Dev. ; Harpides, Cam., 

 Lr. Sil. 



Fam. 17. — Harpesidce.- — Head-shield veiy large and horned, with broad, finely punctured border. 

 Typ. gen. : Harpes, Up. Sil., Dev.; Harpina, Lr. Sil. 



Note. — The section in which these families are placed is named after one of their more striking 

 characters, the band or fillet which connects the eyes with the sides of the glabella; but they have 

 also other points of agi'eement, as seen more especially in their numerous bodi'-segments, their 

 narrow axis and small pygidium. Through Harpides, the Harpesidiv proper are connected both with 

 Arethusina and with Olenus. 



Sub-Order IV. — FEONTONES. — Trilobites with large or sti-ongly pronounced glabella, widening as 

 a rule anteriorly. Pygidium very small or of moderate size, the many-ringed body-axis 

 extending quite or nearly to its extremity. 



§ 1. Annulati. — Many-ringed, comparatively elongated forms, with fiygidium obscurely separated 

 from the thorax. Bodj^-segments tj^pically 1 1 in number. Facial sutures terminating at the 

 sides of the head-shield. 



Fam. 18. Phacopsidœ. — Pleurœ furrowed. Eyes coarsely facetted. Pygidium rounded or spinose. 

 Typ. gen. : Phacops, Up. Si!., Dev. ; Dalmanites, Sil. ; Odontocephalus, Dev. 



Fam. 10. Encrinuridœ. — Pleurœ with raised band. Pygidium long, nari'ow, with many-ringed axis. 

 Typ. gen. : Encrinurus, Sil. ; Cyhele, ILv. Sil. ; Gromus, Uj). Sil. ; Amphion, Lr. Sil. 



