354 Mr. II. Sccley 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 vertebras 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 vertebras, twenty-one 

 of which, measuring 2 feet 1-A- 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 vertebras 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 

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

 and more circular. The caudal vertebras are shorter than those 

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

 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 vertebras with their interspaces measure 4A- 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 

 23f inches, while the hind limb is 24 inches long. 



The humerus measures 8f inches long, is 3-f- 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, subscapulars, 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^ inches long and 2^ inches wide, and 2-jV inches long in 



