454 



SMITHSONIAN MISCEI.LANEOUS COLLECTIONS 



VOL. 52 



to those of the vertebra just described, but longer, both transversely 

 and antero-posteriorly, with a long and deeply concave articular 

 facet at the extremity. There is no facet on the body of the vertebra 

 for the articulation of the head of a rib. The body itself resembles 

 that of the vertebra previously described in form and size, but the 

 epiphyses are elliptical, rather than cordate. 



The dimensions of the vertebrae are as follows : 



Dimensions of three vertebrce of Prosqicalodon australis. 



Greatest length of centrum , 



Greatest depth of centrum . , 



Greatest breadth of centrum 



Breadth, including transverse processes 



Length of transverse process. 



Least breadth of transverse process antero-pos- 

 teriorly 



Greatest diameter of transverse process at ex- 

 tremity 



Breadth of neural canal 



Height of neural canal anteriorl}' 



Breadth of neural spine antero-posteriorly at 

 base 



Atlas. 



mm. 

 67 



129' 

 155 



18 



17 

 51 

 67 



Thoracic 

 vertebra 



75 

 68 

 90 



29 



36 



45 

 42 



36 

 57 



Thoracic 



vertebra 



b. 



77 

 69 

 87 



i84(?). 

 39 



52 



51 

 31 . 



1 Across posterior articular facets. The breadth across the anterior facets is the same. 

 - The superior one, from anterior base. 



The jaw and teeth above described confirm many of Doctor Lydek- 

 ker's statements regarding Prosqualodon australis, and especially its 

 size, the small number of teeth as compared with Squalodon, and 

 the peculiar form of these organs. The size of the skull figured by 

 Doctor Lydekker in 1899^ is not given, but assuming that it was 

 about as large as the type skull, it seems likely that the number of 

 two-rooted molar if orm teeth did not exceed ten in the lower jaw. 

 The Patagonian material here described affords us the information 

 that the anterior teeth were single-rooted, as might, of course, have 

 been expected. 



The vertebrse are especially interesting on account of their resem- 

 blance to those of Burhiiiodclplus, a genus which Professor Abel 

 derives from the Squalodontid?c. It is to be observed, however, 

 that the atlas of Squalodon figured by Van Beneden^ is quite differ- 

 ent in form from that of Prosqualodon. The former is much more 



^ Proc. Zool. Soc. London, 1899, p. 919, figs, i, 2. 



^ Rechercher )ur les Squalodons, 1865, pp. 45, 46, pi. 3, fig. 2. 



