52 Mr. H. Seeley on Plesiosaurus macropterus. 



middle. The length of the radius is 6 inches; its breadth at 

 both the proximal and distal ends is 4| inches, the least dia- 

 meter being 3 inches. 



The ulna is 6 inches long and 4 inches wide. The greatest 

 interspace between it and the radius is 1^ inch, while both 

 above and below they touch. 



The length of the carpals is 4^ inches : there are three in 

 each row. 



The length of the metacarpals and phalanges is 20 inches. 

 There are five rows, and nine bones in each row. 



The femur is a smaller bone than the humerus, though larger 

 at the proximal end, which has a great trochanter. Its anterior 

 border is nearly straight, and the posterior border is much less 

 cupped than in the other limb. It is at least 11 inches long, 

 7\ inches broad at the tibial end, while the proximal end mea- 

 sures in breadth 2>\ inches. 



The tibia is 5 inches long, and the fibula rather less. At the 

 proximal end the tibia is 4 inches broad ; but the fibula is 

 4^ inches broad : like the ulna, it is reniform. 



The length of the tarsals is 4 inches; the length of the meta- 

 tarsals and phalanges 25 inches ; there are nine or ten in each 

 row. 



Thus this species, in the small size of the head, and the small 

 proportion it bears to the length of the limbs, of the neck, and 

 of the skeleton, is as well distinguished as by the number of 

 vertebrae in the different regions of the body. It has four more 

 cervicals than P. dolichodeirus, but three fewer vertebras in the 

 back. There are eight more cervicals than in P. Hawkinsi, and 

 one more dorsal ; one sacral, instead of two ; and but twenty- 

 eight caudal vertebrae, instead of thirty-five*. 



All Plesiosaur vertebra? have epiphyses which are relatively 



* In the Museum of the Yorkshire Philosophical Society is a Plesiosaur 

 with the MS. name P. homalospondylus. Its parapophyses begin to get 

 long, and support enormous ribs, at the 40th vertebra, but do not appear 

 to be entirely supported on the neurapophyses till the 44th. The lower 

 cervicals have two articulations for ribs, and are very elongated, some 

 measuring more than 3 inches in length. The lower jaw, which has lost 

 the articular part, measures 9^ inches long. The total length of the spe- 

 cimen is 1/ feet 6 inches. Therefore its formula appears to be— 



P. homalospondylus. 



Head about one-twentieth of skeleton, and one-ninth of the neck. Ver- 

 tebrae : cervicals 44 ?, dorsals 16 ?, caudals 28. Though nearly resembling 

 our species, and belonging, no doubt, to the same genus, it is readily 

 distinguished. The vertebrae have their margins rounded, and not sharp. 

 The humerus, which measures 12 inches long and 8 inches broad, has 

 the anterior side singularly straight. The femur, which is 12^ inches 

 long and 7? broad, has the whole anterior border concave. 



