10 



UNITED STATES NATIONAL MUSEUM BULLETIN 294 



(transvei-se diameter, 48 mm.) at its anterior end. The 

 vertical portion of this articular surface terminates 

 about 20 mm. below the apex of the olecranon process. 

 The vertical and the more or less horizontal portions 

 of this greater sigmoid articular surface meet at an 

 abrupt angle. Below its ventral anterior margin the 

 articular surface of the greater sigmoid cavity meets 

 at a right angle the hemicircular facet for articulation 

 with the opposing facet on the proximal end of the 

 radius; the vertical diameter of this facet is 30 mm. The 

 curved shaft is compressed from side to side, more 

 noticeably distally than below the radial facet, and is 

 distinctly broader than that of P. caJvertensis. Viewed 

 from the side, the posterior profile is more curved than 

 the anterior profile of tlie shaft. The posterior edge is 

 somewhat thinner than the anterior edge of the shaft 

 and this condition jjersists at the rugose distal end 

 which has the posterior angle extended backward. The 

 distal epiphysis of the right ulna is quite narrow, at- 

 tenuated toward its posterior end and measures 84 mm. 

 in length ; its greatest thickness is 25 mm. 

 See table 8 for measurements of the ulna. 



Table 8. — Measurements {in mm.) of the ulna, USNM 23794 



Right Left 

 Greatest length of ulna (lacking di.«tal epiphysis) 397 400 



Distance from dorsal to ventral end of greater 



sigmoid cavity (in a straight line) 71 72 



Least anteroposterior diameter of shaft (near 



middle of shaft) 55 53 



Least cxterointernal (transverse) diameter of 



shaft (near middle of shaft) 23 23 



Greatest anteroposterior diameter of distal end 



of shaft 95 99 



Greatest extcrointernal (transverse) diameter of 



distal end of shaft 32 37 



MANUS 



The bones of the right manus were lodged under the 

 transverse processes of the second to fifth dorsal verte- 

 brae. The carpals were in close contact with one another 

 and with three metacarpals. The other finger bones 

 were less closely associated. 



C.VRi'.\LS. — Five of the six carpal bones associated 

 with the right forelimb were preserved seemingly in 

 more or less normal relationship at the extremities of 

 the radius and ulna. The irregular roughened circum- 

 ference of these carpals clearly indicates tiiat they were 

 held in position by interposed fibrous tissue. Tlfe inner 

 (flexor) surface of each carpal is considerably larger 

 than the opposite (extensor) surface. The presence of 



a smooth, curved surface on the anterior face of tlie 

 radiale suggests a synovial joint, which may have per- 

 mitted limited movements by the first metacarpal. The 

 other carpal bones are thought to have been incapable 

 of facilitating such movement by the corresponding 

 metacarpals. At least six centers of ossification are rep- 

 resented by individual carpal bones in the right manus. 

 There arc certainly tliree carpals — radiale, interme- 

 dium, and ulnarc — in the first row which when exposed 

 by the preparator were found to be nearly in contact 

 with the detached ossified epiphysis on the distal ends 

 of the right radius and ulna. This pisiform, if present, 

 was not preserved. 



The position and characteristics of these three car- 

 pals show that tentative identifications of carpals of 

 Pelocetii.s cal'vertensis (Kellogg, 1965, pi. 17) were in- 

 correct. On the basis of this Choptank manus the carpal 

 figured as the radiale (ibid., pi. 17, fig. 9) is the inter- 

 medium, and the supposed second row carpal (ibid., 

 pi. 17, fig. 7) corresponds to the radiale. The ulnare 

 (ibid., pi. 17, fig. 8) seems to agree with that carpal in 

 the Choptank carpus. 



The radiale (pi. 4, fig. 13) is the smallest of the three 

 carpals in the first row; a proximodistal compressed 

 protuberance is present on the posterior portion of the 

 roughly sculptured circumference. The smooth surface 

 on the outer (extensor) fac«, which curves upward on 

 the anterior face to the opposite inner (flexor) face of 

 this carpal may indicate a direct articulation with the 

 first metacarpal as in the manus of Squnlodon (USNM 

 22902). In the manus of Balaenoptera nnisculus and B. 

 aeutorostrata skeletons in the U.S. National Museum 

 the radiale, however, is the largest carpal in the first 

 row. 



The intermedium (pi. 4, fig. 14) is the largest of the 

 carpals in the first row, the maximum dimensions of the 

 inner (flexor) surface being 52 and 59 mm. The flat- 

 tened imier face of this carpal is about twice the op- 

 posite more convex outer (extensor) face. The circum- 

 ference of the intermedium is unusually rugose and 

 pitted. 



Tlie quadrangular flat inner (flexor) face of the ul- 

 nare (pi. 4, fig. 15) is about twice the size of the oppo- 

 site oval extensor face; the irregular circumference is 

 likewise rugose and pitted. The greatest diameter of the 

 inner (flexor) face is 46 mm. 



A carpal (pi. 4, fig. 17) as large as the radiale, which is 

 tentatively identified as the centrale, was located in the 

 matrix almost in contact with the distal face of the ul- 

 nare. The outer face is not quite as rugose as the circum- 

 ference of this carpal ; the ovoidal inner (flexor) face is, 

 however, flat. 



