446 SMITHSONIAN MISCELIvANKOUS COLLECTIONS VOL. 52 



If Professor Abel's views^ regarding the origin of the Iniidae be 

 correct, Proinia should show a much closer approximation to Sqiialo- 

 don than does Inia. I do not see that such is the case. The only 

 characters which might be construed as showing a leaning toward 

 Squalodon are, perhaps, the shape of the zygomatic processes and 

 of the median processes of the frontals, and the rather flat basiocci- 

 pital region. Squalodon is in many respects a specialized form, and, 

 in my opinion, hardly to be considered as belonging on the main 

 stem of development. Of known forms, I should prefer to take the 

 point of departure from Agorophius, but Proinia appears to show no 

 closer resemblance to that genus than it does to Squalodon. 



It has to be considered also, as is indicated below, that Proinia 

 occurs with Prosqualodon, a near relative of Squalodon, in the Pata- 

 gonian beds. It can hardly be supposed that Proinia has been de- 

 rived from this form, which appears to be contemporary. The 

 squalodont type and the inioid type appear to have been thoroughly 

 differentiated and well established in the early Miocene, and we must 

 look back further for the progenitors of the latter, as we certainly 

 must for those of the former. 



Other Accompanying Vertebra 



A series of five thoracic vertebrae and a caudal vertebra, No. 1543Q, 

 collected at Darwin Station by Mr. Hatcher, April 22, 1899, might 

 from a superficial examination be considered as possibly belonging 

 with the skull and cervical vertebra of Proinia. It is my opinion, 

 however, that they are rather too small, and they do not exhibit any 

 tangible inioid characters. Most of the epiphyses are detached, 

 showing that the individual was comparatively young ; two of them, 

 which are very thin, have been preserved separately. The anterior 

 metapophyses are much elevated above the centra, horizontal, flat- 

 tened, and continued backward on the sides of the neural arch as a 

 sharp ridge. The neural spines were broad antero-posteriorly, and, 

 except in the caudal, appear to have been strongly inclined backward. 

 The transverse processes are preserved on one or both sides of two 

 of the thoracics. In one case they are flat, broad antero-posteriorly, 

 linear, and not expanded at the extremity. In another thoracic they 

 appear to have been somewhat expanded at the extremity, at least 

 anteriorly. 



All the vertebrae have sharp, thin median inferior carinre on the 

 centra. The latter are shorter than broad, and somewhat pentagonal 



* Mem. Mus. Roy. Hist. Nat. Belgique, 3, 1905, pp. 41 and 123. 



