26 FOSSIL REPTILIA OF THE 



more compressed, as the number of vertebrae shows it to have been longer than in the 

 Iguana or Cj/clodus. The twenty-sixth vertebra is dislocated : the two following are 

 turned upon their side and expose the under part: here the inferior spine has 

 disappeared : the surface is smooth, slightly punctate, gently concave lengthwise, 

 convex transversely. Figure 2 gives a direct side view of the best-preserved ramus 

 (the left) of the jaw : below, in outline, of the natural size ; above, magnified. 

 The extent and upward curve of the coronoid piece (31) most resembles that in the 

 Varanus (Cuvier, loc. cit. pi. 1 6, fig. 8 c) ; but in this genus it is relatively shorter than 

 in the BoUchosaurus, and in other recent Lacertians it is still shorter and more pyra- 

 midal in shape. The extent of the surangular (30), and its length behind the coro- 

 noid, are Lacertian characters : but the outer surface is divided by a longitudinal ridge 

 or angle into an upper and a lower facet, the upper one being slightly excavated: 

 the enamelled crowns of the last four teeth show a simple obtuse shape ; they are 

 chiefly remarkable for their small proportional size. The two dentary bones meet at 

 an acute angle ; that on the right side joins a surangular piece which is con- 

 tinued back to near the articular surface. Allowing a symphysis of the ordinary 

 lacertian proportions, the length of the under jaw may be estimated to have been 

 four centimeters (one inch seven lines), or equal to between four and five dorsal 

 vertebrae. One of the vertical columelliform bones is preserved on the left side of 

 the cranium. 



Parallel with the eighteenth, nineteenth, and twentieth vertebrae lie the remains of 

 a broad, thin, and flat bone (51), with a smooth emargination, and a rough or slightly 

 granulated surface. As the broad, thin, and anteriorly emarginate scapula of the 

 Iguana presents a similar surface, I conclude the part in the fossil marked 51 to be 

 scapula; and the short, thick, subcylindrical, hollow bone (.53), slightly twisted and 

 expanded at both ends, to be the shaft of the humerus : it is shorter in proportion to 

 its Ijreadth than in the existing Lizards, and probably supported a shorter fore-arm and 

 fore-foot ; the whole limb being therefore perhaps more formed for swimming than in 

 the Monitors and Iguanae. 



The ball-and-socket structure of the vertebrae is better adapted to sustain the 

 body on dry land than the biconcave structure ; but the modern Crocodiles, the 

 Amblyrhynchus or marine lizard of the Gallopagos Islands, the Salamander, and even 

 the Lepidosteus amongst fishes, prove it not to be incompatible with aquatic habits. 

 The BoUchosaurus, with a proccelian type of vertebrate structure, and amongst the 

 earliest reptiles that manifested such structure, may well have been a good swimmer 

 and frequenter of the ancient ocean of its epoch, as well as a crawler on dry land. 

 Although the articulations of the vertebrae must have limited if not prohibited rotation 

 or inflection of the spine in the vertical direction, the extent of lateral flexuosity is 

 considerable ; the double curve of the fore part of the vertebral column, preserved 

 in fig. 1, being, if not the natural one assumed in the last struggles of the dying 



