ON PROTEROSAURUS HUXLEYI. 239 



distance in front. They are stout discoidal bones five-eighths 

 of an inch in diameter, "with a deep wide notch apparently on 

 the posterior margin, forming the glenoid cavity for the articu- 

 lation of the humerus. At the inner margin of the notch there 

 is an elevated boss ; and from thence to the front margin there 

 is a widish ridge indicating perhaps the compound nature of this 

 bone, which is most likely composed of both the coracoid and 

 scapula, the glenoid cavity being as usual at the junction of the 

 two elements ; but there is no distinct trace of a suture. There 

 is a straight narrow bone lying with one end in contact with the 

 right .coracoid, which may perhaps be a clavicle. A somewhat 

 similar bone is also in contact with the left coracoid, but in this 

 instance it has in some respects the character of a rib. 



The humerus is one inch long, and is a slightly arched stout 

 bone, with the extremities a little expanded ; the distal end, 

 which is the wider of the two, is fully one quarter of an inch 

 across, while the most constricted part of the shaft is a little 

 more than half that width. The proportional measurements of 

 the humerus in P. Speneri differ considerably from the above. 

 In that species this bone has the extremities extremely wide. 

 One figured by von Meyer (tab. IX.), which is two inches and a 

 half long, has the shaft three-eighths of an inch thick, while the 

 proximal extremity is a little less than nine-eighths of an inch 

 wide, and the distal nine-eighths. In P. Huxleyi the proximal 

 extremity is very little wider than the shaft, and the distal ex- 

 tremity is about twice as thick as the shaft. In P. Speneri the 

 proximal and the distal extremities are three times the width of 

 the shaft. 



The radius and ulna are not by any means slender ; they are 

 about seven-tenths of an inch long, being considerably shorter 

 than the humerus. The radius is not quite so stout as the ulna, 

 and both exhibit a slight sigmoidal curve. The latter is one- 

 tenth of an inch thick at the centre of the shaft, but is a little 

 enlarged at the extremity. 



The hand, including the wrist, is a little longer than the lower 

 arm. There are two rows of carpals, of which, though disposed 

 in nearly regular order, it is not easy to determine the precise 



