220 



THE EXTINCT BATBACHIA, REPTILIA 



portion flat ; its outline describes nearly half a circle, of which the inner portion only is 

 thickened for the articular face of a carpal: the outer distal angle is thus directed back- 

 wards, towards the humerus. The Immoral articular extremity is a single transverse 



plane. 



The idua is broader proximally than the radius, but not so expanded, the extremities 

 being of nearly equal width. The extremities of ulna and radius are well separated. 



Three carpal bones appear to belong to the first row. They are flat and oval, the ulnar 

 the thickest, the radial the largest; the intermedial has six articular faces, and a, marginal 

 border, which was, I suppose, posterior, and completed the inter-osseous space in front. 

 A fourth bone, which belongs either to the second series or to the metatarsals, is elongate 

 ovate with straight parallel borders, both quite thin, the inner the shorter; extremities 

 thickened, rounded inwards. The position of this bone has been, therefore, longitudinal. 



It is probable that the fore-limb was long, though the proximal portions are so much 

 shortened. The powerful muscles of the humerus would otherwise be without object. 

 These muscles, with the peculiar form of the humerus, probably prevented any appearance 

 of an arm in life, and the hand would be nearly sessile. 



There are no remains of hind limbs, though there is no sufficient evidence that they 



have not existed. 



There are three species of the genus Clidastos known to the writer, which (lifter as 



follows : 



Eleventh vertebra (or the first without trace of hypapophysis) with total width to 

 length as 1 to 1.33., the inverted centrum roof-shaped, elevated ; width (total), 2 in. 3 

 lin. Large. C. ICUANAVUK. 



Same vertebra with width to length as less than 1 : 2; inverted centrum, lower, more 

 broadly rounded; total width, 1 in. (i lin. Small. C. PROPYTHON. 



The generic characters are almost entirely derived from the second species named. 



OLIDASTES IGUANA Y r l.TS, Cope. 



Proceed. Acad. Nat. Sci. Phil. 1868, 22:!. Geological Survey, New Jersey, Cook, App. 0. 



In this species the articular face of the zygosphens is inclined at an angle of 46' >, while Unit of the zygapophysis 

 is a little more, horizontal. The posterior zygapophyses are broken off. 



The convex articular face is nearly vertical, meeting the lower plane at a slightly less angle than the upper. It is 

 much more strongly convex fcrarisverseiy than vertically. The neural arch rises from the anterior three-fourths of the 

 centrum, the zygapophysis coming off from the edge of the cup, and the diapophysis from .2 of the length behind It, 

 The zygapophysis is more prominent than the zygosphen, and the sinus between them is floored by a, thin horizontal 

 plate at its fundus. 



The general form of the vertebra is depressed. The Inferior face of the centrum presents a, median obtuse ridge, 

 and nearly flat lateral laces, which are concave antero-posteriorly. 'the cup is broader than deep, and nag a slightly 

 concave outline : the ba.se <>r the zygosphen originates opposite the middle of the neural canal. The latter is a, broad 

 vertical oval. 



