354 Mr. H. Seeley on two new Plesiosaurs from the Lias. 



Each centrum is much higher than long. Thus there are, with 

 two scattered on the slab, twenty-seven cervical vertebrse pre- 

 served ; and if the interspaces represent the number missing, 

 there must have been originally about thirty-six. The hinder 

 cervical ribs are 2 inches long. 



In a former paper on Plesiosaurus macropterus, I adopted as 

 the first dorsal that vertebra in which the rib rises entirely on 

 the neural arch — a view since sanctioned by Professor Owen in 

 his Monograph of Plesiosaurs. 



The length of the dorsal and sacral region in this specimen is 

 2 feet 5 inches, and it includes twenty-four vertebrae, twenty-one 

 of which, measuring 2 feet 1^ inch, have the ribs entirely 

 supported on diapophyses. The remaining three, with large 

 articular facets, may be considered pelvic. The first dorsal is 

 an inch and a quarter long ; but these vertebrse gradually become 

 a little shorter, and the last dorsal measures only l-^^inch. The 

 venous foramina rise to the middle of the side, which is much 

 more concave than it was in the neck. The diapophysial articu- 

 lation is vertical, looks behind, is subelliptical, and in the first few 

 vertebrse more than an inch deep ; but it soon becomes smaller, 

 and more circular. The caudal vertebrse are shorter than those 

 of the back, have flatter sides, and are marked by large hsema- 

 pophysial pits. The ribs are very short, and, like those of the 

 hinder part of the neck, taper to an end in about 2 inches. The 

 four caudal vertebrse with their interspaces measure 4i- inches. 



As in the typical specimens of all the species with which this 

 one presents any affinity, it is the under surface of the limbs which 

 is displayed : those of the right side are in situ ; but on the other 

 side only the femur and humerus remain, the latter showing the 

 upper surface. The fore limb is slightly the shorter, measuring 

 ^S^ inches, while the hind limb is 24 inches long. 



The humerus measures 8^ inches long, is 3^ inches over the 

 radial end, and If inch over the greater part of the shaft. The 

 proximal end is a little contracted and bent backward, and the 

 rough condyle is moderately convex. The under surface is flat- 

 tened and rounded, and displays at an inch below the condyle a 

 slight oblique rough process, probably for attachment of the 

 latissimus dorsi. The anterior border is somewhat straight, 

 being slightly concave below and slightly convex above ; but the 

 posterior border is more deeply and regularly cupped. The 

 superior is rather flatter than the inferior surface, except at the 

 proximal end, which becomes elevated to a trochanteroid thick- 

 ening for the deltoid, subscapularis, and pectoralis muscles, and 

 makes the bone concave in length. The ulna is flattened, and 

 slightly reniform, and a little shorter than the radius, being 

 3-i- inches long and 2-i- inches wide, and 2yV inches long in 



