SYSTEMATIC REVISION 



65 



far out from the sides of the intercentrum for two or three millimeters. 

 The skull resembles that of Trimerorhachis, so far as it is preserved. The 

 animal was about 30 centimeters long." 



Revised description: 



1. Expanded neural spines more nearly flat; the apices of adjacent 



spines closely united, so that the connection is indistinct. 



2. Intercentra with low median keel, the lateral processes prom- 



inent. 



Aspidosaurus apicalis Cope. 

 Cope, Zatrachys apicalis. Am. Nat., vol. 15, 1881, p. 1020; Am. Nat., vol. 18, 1884, p. 36. 



Type: The apices of several neural spines. No. 4785 Am. Mus. Nat. 

 Hist. Cope Coll. From New Mexico. 



Original description: "The summits of the neural spines are expanded, 

 and the superior faces of the expansions are tubercular and have a median 

 prominence. The expansions are sometimes large, resembling the dermal 

 bones of crocodiles, and in that case the median prominence is a keel. On 

 the smaller expansions the latter is a mere apex. There are narrow flat bones 

 which I suppose to be neural spines and which are ornamented with inoscu- 

 lating ridges. A capitular head of a diapophysis is compressed. Intercentra 

 well ossified, those preserved without lateral notch. Inferior surface with 

 crowded small fossae, giving a delicate reticulate relief. Length of an inter- 

 centrum, .013; width of do., .014; width of the summit of a neural spine, 

 .020; length of do., 014; width of a second do., .025; length of do., .015; 

 width of a third (two unite), .034; length of do., .039. The reference of this 

 species is provisional only. It is much larger than the Z. serratus." 



In the second paper Cope added: 



" In the typical species, Z. serratus, the rugosities project in the form of 

 teeth along the external alveolar border. Individuals with sculptured, neu- 

 ral spines and dermal bones are referred here. The intercentra are much 

 like those of Eryops and Acheloma." 



Revised description: Cope's reference of this species was at first uncer- 

 tain; but when he decided to place in the genus all forms with expanded 

 spines and skulls with serrate edges, he placed it in the genus definitely. 



Fig. 15. 



A. A. {Zatrachys) apicalis. No. 4785 



Am. Mus. X I. Top view of spine. 



B. Lateral view of same spine 



C. A. crucifer. No. 171 Univ. of 



Chicago. X I. Posterior view of 

 neura! spine of a dorsal vertebra. 



As has been shown, the skull of Aspidosaurus in no wise resembles that 

 of Zatrachys. The specimen is referred to Aspidosaurus provisionally; the 

 wide geographic separation makes it very possible that when more is known 

 of the creature, it will be found to be generically distinct at least. 



I. Only the apices of the spine known. Flat, oval in outline, with a 

 peg-like apex. Overlapping slightly. 



