ON PROTEROSAURTJS HUXLEYI. 241 



is considerably and rather suddenly enlarged. In this as in all 

 the other bones, the articular extremities, having been formed of 

 cartilage, are wanting, the ends being truncated. It is therefore 

 quite impossible to describe in detail the characters of the joints. 



Fragments, apparently of the right tibia and fibula, and three 

 or four of the phalanges, are scattered about in the vicinity of 

 the bones of the left leg ; but no other traces of the right limb 

 are to be found. 



The only portion of the pelvic girdle present is the extremity 

 of a flat bone. This fragment is three-tenths of an inch long, 

 and two-tenths of an inch wide ; it slightly widens towards the 

 anterior extremity, which is truncated. This is probably a por- 

 tion of the ilium. 



From the above description it seems evident enough that this 

 small reptile is a true Proterosaurus, and that it is specifically 

 distinct from P. Speneri. The long articulating limbs and ex- 

 tensively produced tail are common to both species. In both, 

 too, the neck has been of considerable length, and the number 

 of cervical vertebrae (seven) is apparently the same in both. And 

 the number of the dorsal vertebrae would likewise appear to agree 

 in both species, and in each there are numerous ventral ribs. 

 The same harmony is found in the number and character of the 

 hand-bones. Unfortunately no comparison can be instituted re^ 

 specting the skulls and the individual features of the vertebras, 

 as the parts in the new species are too imperfectly preserved ; 

 enough, however, seems to be known to warrant the assertion 

 that the two are generically coordinate. 



It appears equally clear that the small individual is specifically 

 distinct. The diminutive size alone suggests this, especially as 

 there are no appearances of immaturity ; and the form of the 

 ribs would seem to prove its specific distinctness. In P. Huxleyi 

 we have seen that they are flattened towards the proximal extre- 

 mity, while in P. Speneri they are rounded at this part ; and in 

 the former they are not widened and grooved to anything like 

 the same degree at the distal extremity. 



The limbs, too, are proportionately different. In P. Speneri 

 the fore limb is four inches and seven-eighths long, as figured 



Q 



