Report of the State Geologist, 97 



to be based to an important degree upon the structure of the occi- 

 pital ring of the cephalon, whether it be smooth (or with a central 

 tubercle), unispined, bispined, etc. The variations of this character, 

 upon which the subdivisions Ceratocephala {sensu stricto Trapelo- 

 cera), Acidaspis and Odontopleura depend, is not one of high morph- 

 ological value, but it is not infrequently that variation in such 

 minor details as this has proved of the greatest convenience 

 in a subsidiary classification of the trilobites, for example, among the 

 Phacopidse and the Proetidee. In the entire group of Ceratocephala 

 there is no more important variation in essential characters than that 

 of the anchylosis of the cheeks with the cephalon in Acidaspis Ver- 

 neuili and its allies, and the confluence of the lateral glabellar lobes 

 in A. Buchi. 



The usefulness of the subdivision proposed in the following lies 

 primarily in the homogeneity of the groups and secondarily in the 

 fact that it retains in their original value names of long standing. 



Scheme of Classification. 

 Genus Ceratocephala, Warder, 1838 : 



Glabella with a long central lobe extending from near the anterior 

 margin of the cephalon to the occipital ring; lateral lobes in two pairs, 

 generally quitie distinct from the central lobe. The facial sutures 

 originate just within the genal angles, passing over the ocular nodes 

 and cutting the frontal margin where their anterior terminations are 

 separated by the width of the glabella ; rarely obsolete from 

 coalescence. Eyes small. Thoracic segments generally nine, some- 

 times ten; extremities of the pleurae produced into spines. Pygidium 

 with two or three annulations. Margins of cephalon and pygidium 

 and surface of the test generally abundantly supplied with spines. 



Type, Ceratocephala goniata, Warder. 



1. Species having the occipital ring 



(a) Smooth or with a central tubercle. 

 Odontopleura, Emmrich. Type, 0. ovata, Emmrich. 



(b) With a single, large, straight, median spine. 

 Acidaspis, Murchison. Type, A. Brighti, Murchison. 



Synonym, Acantholoma, Conrad. 



(c) With two straight, divergent spines. 

 Ceratocephala, Warder, sensu stricto. Type, G. goniata, Warder. 



Synonym, Trapelocera, Corda. 



(d) With two spirally recurved spines of great size. 

 DicRANURUs, Conrad. Type, D. hamatus (Conrad), Hall. 



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