596 



PROF. H. G. SEELEY Olf THE 



ulna thickened ; it is in close contact with the other two bones 

 which are placed distally. On the ulnar side there is a foramen 

 between this bone and the element which is above the fifth digit, 

 and separated from it by a cartilaginous interspace. On the radial 

 side there is a close sutural union with the bone, beneath which are 

 placed the four carpals of the distal row. There is an interspace, 

 which was presumably occupied by cartilage, between the distal 

 end of the radius and the carpal above the first digit. The bone on 

 the ulnar side is obviously the cuneiform. But that on the radial 

 side may be either the scaphoid or centrale. Prom its holding a 

 corresponding position to the naviculare of the tarsus in relation to 

 the bones of the distal row, there is some evidence in support of its 

 identification as the centrale, in which case the scaphoid is unossi- 

 fied, but the evidence is insufficient to determine the point, especially 

 as there is an interspace between the distal carpal bones and this 

 element. If the bone were identified as the scaphoid it would 

 approximate the carpus towards such a mammalian type as 

 Cheiromys; and the resemblance would be not less interesting if 

 the scaphoid were supposed to be unossified on the radial side, and the 

 pisiform unossified on the ulnar side. In any case the condition is 

 unlike that of Plesiosaurs, in which the carpal bones of the proxi- 

 mal row have a transverse linear arrangement. Lariosaurus is 

 figured by Zittel with two bones in the proximal row and two in 

 the distal row, but the carpus is imperfectly known in Neusticosaurus 

 and unknown in Anarosaurus. 



The distal row of the carpus in Mesosaurus Q,onsis,i& of four bones/ 

 arranged like the corresponding bones in a mammal. They are 

 identified as trapezium, trapezoid magnum, and unciform. The 

 first of these is the smallest, and the unciform is the largest. 



The metacarpus consists of five divergent bones which vary in 

 length. The first is strong and short, J centimetre long. The 

 third, fourth, and fifth are about |^ centimetre long, and the fifth 

 (which is most slender) is only a little longer than the first. The 

 transverse measurement over the distal ends of the metacarpal 

 bones is fully 1| centimetre. The digits are moderately developed, 

 the middle digit being the longest ; and in every case the first 

 phahmge is the longest and strongest. The digits terminate 

 in short conical claws. The number of phalangeal bones is 

 2-3-4-3 + -3-I-. The fourth digit is imperfect ; the fifth has three 

 well-developed phalanges without a terminal claw, and a small 

 ossification lies near its extremity which may represent the rudi- 

 ment of a terminal phalange. The first digit, including the meta- 

 tarsal, measures fully | centimetre, and the third measures 1| 

 centimetre in length. 



There are obvious differences between this specimen and the 

 type, but it is difficult to judge of their importance. In the Paris 

 fossil the teeth appear to be more numerous, but in both they have 



^ Attention is subsequently drawn to the specimen of Sfereosternum which 

 may possibly show five bones in the distal row of the carpus. 



