CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



11 



The carpal (pi. 4, fig. 16) tentatively identified as the 

 trapezoid is elongated (length, 54 mm.) ; its width pos- 

 teriorly (34 mm.) is equivalent to the outer-inner (ex- 

 tensor-flexor) diameter. The elongated outer (extensor) 

 face is noticeably flattened in contrast to the irregularly 

 depressed inner (flexor) face. This carpal was present 

 in the second row distal to the interval between the 

 radiale and the intermedium. 



An ovoidal (38X35 mm.) carpal (pi. 4, fig. 18) that 

 lias smooth flattened inner and outer surfaces and a ru- 

 gose circumference, whose maximum thickness (21 mm.) 

 is less than half the corresponding measurement 

 (44 mm.) of the intermedium, obviously was shifted 

 behind the ulnare from its original position in the 

 manus. It may have been either the unciform or the 

 magnum. 



Metacarpals. — Four metacarpals were associated 

 with the right forelimb and one with the left. The two 

 identified as the third and fourth lay distal to the carpal 

 thought to be the centrale. The first metacarpal was 

 found distal to the radiale. The second metacarpal was 

 misplaced and lay on the adjoining ulna. The shafts 

 of all the metacarpals are thicker, more cylindrical and 

 less compressed in an extensor-flexor direction than 

 those of Pel-ocetus ccdvertensis (Kellogg, 1965, pi. 18). 



The shortest metacarpal (pi. 4, fig. 5 ; length, 63 mm.) , 

 which was embedded in the matrix distal to the radiale, 

 is identified as the first. The triangular proximal end is 

 about twice as large as the distal end ; the shaft is some- 

 what narrowed distally and its anterior face is thicker 

 than the compressed posterior face. Both ends are rather 

 smooth and lack distinct rugosities for attachment of 

 cartilaginous connections. 



The metacarpal (pi. 4, fig. 1 ; length, 95 mm. including 

 epiphysis) tentatively identified as the second, has an 

 ossified proximal epiphysis which was not fused with 

 the shaft. Before being covered with sediments this bone 

 had been dislodged and moved to the anterior side of 



Table 9. — Measurements [in mm.) of the metacarpals, USNM 



23794 



the flipper. The distal end of the shaft is more com- 

 pressed in an extensor-flexor direction than the proximal 

 end and is pitted for attachment of cartilage. 



The third metacarpal (pi. 4, fig. 2; length, 90 mm.) 

 and the fourth metacarpal (pi. 4, fig. 3 ; length, 78 mm.) 

 seem to have retained their normal position in the flip- 

 per distal to the intennedium and ulnare. The proximal 

 end of the third is oval and that of tiie fourth almost 

 quadrangular; their distal ends are wider and more 

 compressed in an extensor-flexor direction than their 

 proximal ends. Both ends of each metacarpal are rugose. 



See table 9 for measurements of the metacarpals. 



Phalanges. — Four phalanges were associated with 

 the right forelimb and only one with the left. Two (pi. 

 4, figs. 9-10) of these phalanges are rather slender and 

 not flattened except distally ; they seemingly represent 

 the same bone in the first finger of opposite flippers. At- 

 tached to the proximal end of the phalange in the right 

 flipper is a lump of ossified cartilage. The largest pha- 

 lange (pi. 4, fig. 6; length, 62 mm.) is distinctly 

 flattened in an extensor-flexor direction, expanded more 

 transversely at the proximal than at the distal end, both 

 ends being roughened for attachment of connecting 

 cartilage. Both of the subterminal phalanges (pi. 4, figs. 

 7-8) are compressed in an extensor-flexor direction, the 

 shortest bone (length, 46 mm.) being nearest the end of 

 the finger. 



See table 10 for measurements of the phalanges. 



Table 10.- 



-Measurements (in mm.) of the phalanges, 

 USNM ZS794 



VERTEBRAE 



CERVICAL VERTEBRAE 



The atlas, axis, third, fourth, fifth, and sixth cervicals 

 were excavated with this skeleton (USNM 23794). On 

 the right side of the axis and of the third cervical the 



