56 MAURICE G. MEHL 



centra differ but little in size from those of the dorsals. The 

 vertebra figured and described as a dorsal of C. prenasalis is appar- 

 ently very similar to the anterior caudals of C. Visheri and may 

 well belong to the caudal series. This being the case, the vertebrae 

 of the two forms are not very different. 



The remains of C. Visheri represent a creature approximately 

 five and a half feet from tip to tip. The skeleton is probably not 

 that of a young individual, but it is possible that it had not reached 

 its greatest length. It is probably a good average for the species, 

 and is apparently somewhat smaller than C. prenasalis. 



While any record that indicates the former distribution, the 

 relative abundance, and the diversity of the extinct Crocodilia is 

 noteworthy, there is, perhaps, a special interest in the form here 

 described in the light that it throws on the ancestry of the caimans. 

 To the writer's knowledge, there is no record of extinct caimans and 

 the history of the alligators is almost as obscure. While the genus 

 Caimanoidea is perhaps too highly specialized in the external 

 narial opening to stand in the direct line of the caimans, in other 

 respects, especially the moderate size of the supratemporal fenes- 

 trae, it is very similar to what one would expect in their primitive 

 ancestors. The genus stands close enough to the modern forms to 

 indicate a very ancient history for this group. 



The writer wishes to take this opportunity to thank Professor 

 Over, through the courtesy of whom he was permitted to study the 

 material here described, and President C. C. O'Harra of the South 

 Dakota School of Mines for the loan of the type skull of Caiman- 

 oidea (Crocodilns) prenasalis. The writer is also greatly indebted 

 to Professor Ruthven, director of the zoological museum, Uni- 

 versity of Michigan, for the loan of caiman material and for 

 valuable information concerning that group. 



The type of Caimanoidea Visheri is number 1,044 in the Uni- 

 versity of South Dakota geological collections. 



