NO. 1875 



NEW FOSSIL CETACEAN — TRUE 



445 



vertebrarterial foramen, which is elHptical and very large, and was 

 complete originally. The base of the portion of the process below 

 the foramen is thick and nearly horizontal, while the terminal portion 

 is expanded and rather thin, and is nearly vertical, but a little in- 

 clined forward below. The portion above the foramen is slender and 

 nearly cylindrical. The process as a whole resembles that of Inia, 

 but in that genus the vertebrarterial foramen is incomplete. 



The centrum of the vertebra of Proinia has a median ridge supe- 

 riorly and inferiorly, while the sides opposite the vertebraterial 

 foramina are deeply concave. The anterior epiphysis is slightly con- 

 vex and the posterior one a little 

 concave. Both are anchylosed to 

 the centrum and are thin. 



The dimensions of the vertebra 

 are as follows : Length of centrum, 

 31 mm.; breadth of centrum, 51; 

 depth of centrum, 46; greatest 

 breadth of vertebra across trans- 

 verse processes, 108 ( ?) ; greatest 

 height from inferior margin of 

 centrum to tip of neural spine, 

 85; height of neural canal, 30; 

 breadth of the same, 51 ; length 

 of neural arch in the median line 

 above, 18; distance between tips of anterior and posterior zyga- 

 pophyses on either side, 50; length of anterior zygapophysis, 15; 

 breadth of the same, 14; length of posterior zygapophysis, 19; 

 breadth of the same, 15; height of vertebrarterial foramen, 24; 

 breadth of the same, 17. 



Without more complete material, it appears to me unwise to 

 attempt many generalizations as to the origin and relationships of the 

 form here described. It is much larger than Inia, and that it is 

 quite distinct will, I think, be conceded ; as also that it is rather closely 

 related to the latter genus, warranting its assignment to the family 

 Iniidse. I am unable to see that it throws any considerable light on 

 the origin of this family, although it is in some respects less special- 

 ized than Inia. As compared with the latter, generalized characters 

 are observable in the thin walls, large size, and only moderately an- 

 terior position of the orbit ; the larger extension of the frontals at the 

 vertex; short postorbital process; moderately large temporal fossae, 

 and perhaps the flat basioccipital and the meniscoid zygomatic pro- 

 cesses ; also in the length of the cervical vertebrae. 



Fig. 76. — Third cervical vertebra of 



Proinia patagonica, new species. 

 Anterior surface. One-half nat. size. 



