68 REPORT— 1839. 



of eight instead of six ossicles, as in the PL Haivkinsii. The 

 fourth or additional one in the first or proximal row is wedged 

 in between the ulna and the third carpal bone, at the outer an- 

 gle of the carpal joint ; it is much smaller than the rest. 



The relative sizes also of the three normal bones of the first 

 row is different ; in the PL Hawkindi the middle one is the 

 largest, the radial or anterior one least : in the PL niacroce- 

 23halus the ulnar or posterior of the three is, if anything, the 

 largest, and the radial bone not so much smaller than the other 

 two. The disproportionate size of the two posterior bones in 

 the PL Hawkinsii compensates for the shortness of the ulna. 

 In the distal row of the carpus the superadded bone in PL ma- 

 crocephalus is a very small ossicle wedged in between the third 

 or posterior carpal, and the fifth or ulnar metacarpal bones. 



The metacarpal bones correspond with those of PL Hmvkin- 

 sii ; the radial or anterior one, which corresponds to the pollex, 

 being the shortest and broadest. 



PL 7nacrocephalus* . PL Hawkinsii. 



The 1st or radial metacarpal supports 2 (but probably 3 phalanges) 3. 



The 2nd metacarpal 6 6or7? 



The3rdditto 9 8 or 9 ? 



The 4th ditto 8 .'. 8. 



The 5th ditto 6 6*. 



The evidently natural curve formed by the distal phalanges in 

 Lord Cole's PL 7nac7r}cephahis indicates that the paddles were 

 more flexible at their tapering extremity than those of the mo- 

 dern Cetacea. 



Pelvic Extremity. — The femur in PL macrocephalus is re- 

 latively longer than in PL Haivkinsii or dolichodeirus. In the 

 latter it equals the humerus in length ; in the former it exceeds 

 the same bone by one eighth. 



In the PL macrocephalus it is rather more expanded at the 

 distal extremity than in the PL Hawkinsii, but the difference 

 of form is not so well marked as in the humeri of these two 

 species. The bones of the leg have the same distinguishing cha- 

 racter as those of the fore-arm ; and the fibula, in all the Plesio- 

 saurs, corresponds to the ulna in its peculiar bent figure. 



In the PL macrocephalus the fibula is, however, relatively 

 broader than in the PL Haivkinsii, notwithstanding that, like 

 the ulna in the fore-arm, its distal extremity is on the same plane 

 with that of the adjoining bone. It is, in fact, fully as broad as 



* In the enumei-ation of phalangeal bones by Mr. Conyheare (GeoL Trans. 

 1824, p. 387,) the metacarpals are included; allowing for this, the perfect di- 

 gits of the PL dolichodeirus correspond in number with PL HawJcinsii and 

 macrocephalus. 



