CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 

 Table 13. — Measurements {in mm.) of the lumhar vertebrae, USNM gS794 



17 



(pi. 11, fig. 1 ) , which rises 152 mm. above the roof of the 

 neural canal, also mark the commencement of the Imn- 

 bar series. The thin dorsoventrally compressed para- 

 pophyses otherwise do not differ materially in shape 

 from those of the twelfth dorsal. The neural canal is 

 higher (42 mm.) than wide (35 mm.) and a prominent 

 longitudinal median ridge extends the length of -the 

 floor of the neural canal. Neither pre- nor postzygapo- 

 physial facets are present; both metapophyses (pi. 10, 

 fig. 2) are compressed from side to side, slope obliquely 

 downward from external to internal edges and project 

 forward beyond the level of the anterior fac« of the 

 centrum. No protruding bony excrescences are present 

 on this lumbar. 



Second lumbar. — A reduction of the distance (415 

 mm.) between the extremities of the parapophyses and 

 an increase in the minimum anteroposterior length (68 

 mm.) of the thin pedicle of the neural arch are the most 

 obvious features distinguishing this lumbar (USNM 

 23794) from the preceding vertebra. No increase in the 

 height of the backward slanting distal ly truncated neu- 

 ral spine (pi. 11, fig. 2), which rises 145 mm. above the 

 roof of the neural canal, is observable. Each dorsoven- 

 trally compressed, elongated, subspatulate, and narrow 

 (minimum width, 60 mm.) parapophysis (pi. 10, fig. 3) 

 tapers to its rounded extremity. The metapophyses 

 (pi. 9, fig. 2) rise 60 mm. above the floor of the neural 

 canal. A rudimentary median ventral longitudinal ridge 

 is present on the centrum. A prominent median longitu- 

 dinal ridge extends the length of the floor of the neural 

 canal. No bony excrescence is developed on this vertebra. 



Third lumbar. — Downward pressure collapsed the 



left pedicle of the neural arch (pi. 9, fig. 3), tilting the 

 neural spine leftward, and deforming the neural canal. 

 Except for the extremity of the thin left parapophysis 

 (pi. 10, fig. 4) this vertebra (USNM 23794) is other- 

 wise complete. The thin pedicles of the neural arch sup- 

 port the elongated metapophyses which project for- 

 ward noticeably beyond the level of the anterior face 

 of the centrum. The backward slanting neural spine 

 (pi. 11, fig. 3) rises 138 mm. above the roof of the neural 

 canal. A distinct median longitudinal ridge is developed 

 on the dorsal and ventral surface of the centrum. The 

 profile of the anterior end of the centrum is subcircular. 



Fourth lumbar. — ^This lumbar (USNM 23794; pi. 

 10, fig. 5) lacks the distal end of both parapophyses, 

 but is otherwise complete. No bony excrescences are 

 present. The curvature of tiie anterior and posterior 

 edges of the basal portions of these transverse proc- 

 esses show that they were shorter but similar in shape 

 to those of the preceding lumbar. The high neural spine 

 (pi. 11, fig. 4) , which rises 185 mm. above the roof of the 

 neural canal, is bent leftward, deforming the neural 

 canal, but not aflfecting the forward projection of the 

 elongate metapophyses. The posterodistal angle of the 

 neural spine as a result of this strong slant extends 

 backward to less than 10 mm. from the level of the 

 posterior face of the centrum of the fifth lumbar. The 

 anteroposterior diameter (70 mm.) of the thin pedicle 

 of the neural arch has increased. An accentuated median 

 longitudinal ridge is developed on the ventral face of 

 the centrum. 



Fifth lumbar. — As compared with the preceding 

 lumbar, the width and vertical diameter of the centrum 



