532 S. W. WILLISTON 



save the external condyle and a part of the lower portion of the crest. 

 Its resemblance to the femur of Cacops is close, but, like the humerus, 

 differs in its greater stoutness. The adductor crest is heavier, and not 

 as deep, the shaft is distinctly stouter. The articular surface for the 

 tibia is rather better defined than in any of the specimens of Cacops 

 examined. The surface is flattened, or with a gentle antero-posterior 

 convexity with sharp rims. It is broadest on the inner side, narrower 

 in the middle, and again somewhat expanded from before back on 

 the outer side. The surface looks backward at an angle of about 

 forty-five degrees from the longitudinal plane of the bone, with a light 

 obliquity inward. 



A large part of the left innominate bone is preserved, enough to 

 demonstrate its close resemblance to the corresponding element of 

 Cacops. Nor do the proximal ends of the tibia and ulna differ 

 materially; like all the other parts, they are stouter. 



The relationships between Dissorophus and Cacops are very 

 evident, so evident, indeed, that for some time I was in doubt of their 

 generic distinction. It would seem, how^ever, that the much greater 

 development of the carapace in Dissorophus together with the presence 

 of the very large shield, which seems to be entirely absent in Cacops, 

 together with other differences in skull and pectoral girdle, is amply 

 sufficient to separate the two forms generically. And it is also evident 

 that these two genera, presenting the unique characters they do, are 

 entitled to a higher rank than genera. The characters of the family 

 Dissorophidae I have already given, as based upon Cacops and 

 Dissorophus. Whether or not the genus Aspidosaurus Broili should 

 be placed in the same family is a matter of doubt. So far as the 

 carapace is concerned the differences seem radical, in the absence of 

 spinous expansions of Aspidosaurus, the dermal shields forming a 

 shingle-like imbrication. However, other characters, so far as the 

 known details furnished by the type specimen of Aspidosaurus are 

 concerned, seem very like those of this family, and it is possible that 

 the family characters may have to be emended in the future to include 

 Broih's genus. 



Although the know^n remains of Zatrachys are yet very meager, 

 it would seem certain that the genus cannot be included with Dis- 

 sorophus, and that the family Zatrachydidae will find eventual justi- 



