32 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 63, 



LUMBAK A'ERTEBRAB. 



Four lumbar vertebrae (pi. 10, Nos. 12-15) are preserved, but two 

 are incomplete; the second lacks the posterior end of the centrum 

 and its epiphysis, and of the third only the neural spine remains. 

 The centra of two of these lumbar vertebrae, one of which is prac- 

 tically complete with the exception of some defects due to crushing, 

 were utilized in restoring the second vertebra of the series. They 

 are all considerably longer than broad, and, although the fourth 

 lumbar is the longest, no conspicuous increase in the length of the 

 centra between the first and fourth is apparent. The centra are 

 roughly cylindrical in outline. Inferiorly the centra of the first and 

 second lumbars show a tendency to develop a median keel. This is 

 evidenced by depressed areas on each side of the centrum below the 

 transverse processes. The fourth centrum has a well developed keel 

 which is more pronounced at the middle than at either end. A pair 

 of grooves meeting mesially at the keel and directed obliquely outward 

 and backward pass below the posterior margin of the transverse 

 j)rocess and characterize the fourth lumbar. 



The neural spines of the vertebrae of this fossil porpoise, if they 

 were arranged in regular serial order and position would describe 

 a gentle curve arising from the first dorsal and declining from the 

 fourth lumbar. These neural spines, viewed laterally, are strongly 

 flattened, rather squarely truncated on their upper extremities, and 

 vertical in position. The neural arch is preserved on three of the 

 four lumbars. The arch is very broad antero-posteriorly, with 

 concave anterior and posterior margins. The posterior margin of 

 the neural spine is slightly concave. The spine is broader antero- 

 posteriorly than the neural arch, and slightly expanded at the tip. 

 Tlie metapophyses are situated a little nearer to the free edge of the 

 spine than to the centrum and are directed obliquely upward and 

 forward. 



There is no distinct process for the prezygapophysis. The prezyga- 

 pophysial facets (pi. 15, fig. 6), which are formed on the superior 

 face of the upturned margin of the laminae in front of and below 

 the point where the metapophyses arise, are concave, and look 

 upward, inward, and forward. The postzygapophyses are laterally 

 convex, and look downward, outward, and backward, but do not 

 overhang the posterior face of the centrum. The transverse proc- 

 esses (pi. 10, Nos. 12-13) are broad, flattened, and project horizon- 

 tally outward. They are also moderately long, very thin, and 

 expanded (pi. 10, No. 15) at the distal end. This type of lumbar 

 characterizes the genus Platanista. 



