NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 



159 



two Species of this genus can be determined from described material and is 

 now inclined to be in doubt whether even this distinction can be made, 

 though there can be little doubt that more than one species was present in 

 the fauna. The species hypantricus was established by Cope upon the pres- 

 ence of small spout-like processes extending forward from the anterior edges 

 of the neural canal. In the collection from Brier Creek vertebras otherwise 

 indistinguishable may be separated by the presence or absence of the process, 

 but it is far from clear whether these are lost in some cases by accident, or 

 may be present in one part of the column and absent in another. 



Skull (fig. 32). — In common with most of the specimens recovered, the 

 bones of the skull were macerated apart in most cases. The tops of two skulls 

 were found together, and in one, No. 3001,^ the sutures can be clearly made 

 out and establish the position and shape of the bones as described by Case 

 and Broom. 



Fig. 32. — Cricotus heteroditus Cope. X %. No. 3001. Upper surface of skull, showing sutures, /.frontal; 



p, parietal; ptf, postfrontal; pto, postorbital; sq, squamosal; tb, tabulare; so, supraoccipital. 

 Fig. 33. — Cricotus sp. X K- No. 3029. Outline of inner surface of large jaw. 

 Fig. 34. — Cricotus sp. X %. No. 3418. Fragment of a jaw, showing form of teeth. 



One large jaw (fig. 33) nearly 300 mm. long is nearly complete, lacking 

 only the articular region. Unfortunately it was covered by a most refractory 

 matrix, which makes it impossible to work out the sutures. The jaw, No. 

 3029, is very high posteriorly, with a strong coronoid region, but becomes 

 very slender anteriorly. On the inner surface the posterior Meckaelian 

 opening is very large; anterior to this there is a single, smaller opening. 

 The walls of the jaw, surrounding the Meckaelian cavity, are relatively 

 thin, permitting a large amount of fracturing. So far as can be made out, 

 the splenial enters into the symphysis and forms the lower part of the 

 anterior end of the jaw and the inner wall of the dental groove, at least 

 in the anterior half of the jaw. In the anterior half of a small jaw. No. 

 3045, the outline of the bone is clearly shown. Near the middle of the dental 

 series of the large jaw there is a small patch of teeth on the inner wall of the 



° In this article all numbers given, unless otherwise stated, refer to the collection of the University of 

 Michigan. 



