4o8 S. W. WILLISTON 



ARRIBASAURUS, A NEW GENUS OF THEROMORPH REPTILES 

 FROM NEW MEXICO 



Among the collections made by Mr. David Baldwin for Professor 

 Marsh more than thirty years ago, there is a considerable quantity 

 of more or less broken and fragmentary bones of a small reptile 

 from El Cobre Canon, New Mexico. All of this material, or at least 

 the greater part of it, was evidently collected from the surface at one 

 spot where it had been washed from some bone-bed. The material 

 consists, apparently, of the remains of a single species, represented 

 by the bones of adults and young. Among the collections made by 

 the University of Chicago expedition to the same region in the sum- 

 mer of 191 1, there are a number of bones and fragments of bones 

 collected from the surface near the west part of the same canon, 

 that evidently are of the same species as some if not all the remains 

 of the Yale collection, if not also of the American Museum collec- 

 tion made by Baldwin for Professor Cope from El Cobre, which 

 includes the type of the species Dimetrodon navajoicus Case. I 

 should feel quite confident that the Chicago collection came from 

 the same bone-bed deposit as the remains preserved at Yale Uni- 

 versity, were it not that the bones all seem to belong to a single 

 individual, save for a small femur of a yet unnamed cotylosaur of 

 very small size. Of the Yale material the larger part consists of 

 the remains of immature animals, as shown by their smaller size 

 and incomplete ossification of the ends of the long bones. There 

 are, however, portions of the skeletons of at least two adults among 

 the collection. The lower end of one of these adult specimens 

 agrees so well with the humerus figured and described by Case 

 under the name Dimetrodon navajoicus, that I feel fairly confident 

 of their specific identity, notwithstanding the apparent absence of 

 an ectepicondylar process in the specimen as figured by Case. 

 That all this material at Yale and at Chicago belongs in a single 

 genus there can be no reasonable doubt. If the adult specimens 

 are later shown to belong to a distinct species it will be time enough 

 to give a new name when the facts are known. The genus may 

 therefore be defined as follows: 



Arribasaurus, genus new. Teeth slender, conical, more elongate 

 anteriorly, short and closely placed posteriorly. Spines of verte- 



