ON TRTLOBITES. 117 



prove to be a divergent character, but Uic actual imniber of these is at present uncertain, and in the 

 closely related Dorypyge tho thorax is entirely unknown. 



§ n. Palmati. — Broad-formed ti-ilobitcs, with lar^e, sliort-axod, i-adiatel^'-fiirrowed ]\ygidium. 

 Fam. C). Lichaddœ. — Pleuiœ furrowed. P3-gidiiim with short, broad axis and deeply indented 

 mai'gin. Typ. gen. : LicJias, Sil. 



Fam. 7. Bronteidœ. — Pleurte wiih slightly raised suiface-liand. P^-gidiuni with very short axis and 

 entire margin. Typ. gen.: Bronfcus, JjY. iii\., T)e\\ 



§ 4. Cor.u.MNATi. — Trilobitcs of more or less oval form, with largo pygidium, the axis of which is 



typically long, prominent and many-segmented. 

 Fam. 8. PAaefowic/o;.— Glabella short, conical. Bodj-axis comparatively nairow. Pygidium in 



some cases with digitated outline. Typ. gen.: Phaeton, Sil., Dev. ; Dechenella, Dev. ; 



Brachymetopus, Carb. 



Fam. 9. Proetidœ. — Glabella large, smooth or furrowed. Bodj-axis comparatively broad. Axis of 

 pygidium typically with 10 or more pseudo-segments. Typ. gen.: Proetus, Sil, Dev.; 

 Phillipsia, Dev., Carb. ; Grifflthides, Carb. 



Note. — The famih* of the Proetida-, as commonly recognized, includes under the genera Proetus 

 and Phillipsia forms of marked dissimilarity of aspect, so far, at least, as regards the glabella and to 

 some extent the relative width of the body-axis. Whilst in Proetus 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'us strwtus, 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 Dechenella and in Brachymetopus, commonly placed under Phillipsia, there is a similar 

 departure, as regards the glabella, from the t3'pical generic form '. I have, therefore, separated these 

 types with short glabella from the genera with which they are commonly associated, antl have placed 

 them in a distinct family. 



Sub- Order III. — CONIFRONTES. — Trilobites 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 j)ygidium. The latter, typically, of moderate size, or small. Glabella: coniform, 

 contracted (or not expanded) anteriorly. 



§ 1. LoNGicoNi. — Glabella comparatively large, extending to, or nearly to, the anterior margin of 

 the head-.shield. Facial sutures terminating at the genal angles. 



Fam. 10. Horn alonot idee. — Longitudinal furrows feebly indicated. Glabella: flat, typically unfiirrow- 

 ed. Typ. Gen. : Homalonotus, Sil., Dev. ; Buniiekteria {■= H. armatus and other spinose 

 forms), Dev. 



Fam. 11. Calymenidce. — Thorax, pygidium and glabella, strongl}^ lobed. The glabella tapering 

 anteriorly. Typ. gen.: Calymene, Hil.; Ne,se^tretus, Ca.ni. 



Fam. 12. Triarthridœ. — Glabella of neaidy uniform width, with side furrows. Bodj' segments l-l to 

 15 in number. Typ. gen. : Triarthms, Lr. Sil. 



Note. — Homalonotus, commonly jilaced under the C'alymenidœ, is here sejjarated on account of 



' No doubt a series of intermediate varieties might be found in which the distinction becomes gradually 

 lessened or obscured ; but couneoting .series of this kind may be traced more or leas everywhere, and if rigidly 

 followed out would render generic distinctions practically impossible. 



