124 



species it is much longer than the centrum and neural spine, and as long as 

 4.5 centra adjacent. All the haemal arches are directed obliquely posteriorly. 



Although I do not possess any specimen with complete vertebral col- 

 umn, an approximate idea of its length may be gained by comparison of parts 

 which are more or less complete in different species. The cervicals are all 

 preserved in a specimen of Clidastes propytiion from Alabama, and number 

 eight, 1 including atlas and axis. In the type-individual of C stenops, seven 

 may be counted ; in a Platecarpus ictericus, seven ; in a Liodon dyspelor, seven ; 

 of which the last two are without free hypapophyses, while in the two species 

 preceding, but one without the free bypapophysis is preserved. In Cuvier's 

 Mosasaurus giganteus, the dorsals number forty-three; in an undetermined 

 Liodon, from Kansas (alluded to in a former article as L. lutispinus), there 

 are preserved the seven terminal dorsals and thirty-two caudals, with diapoph- 

 yses, which exhibit little diminution in size; the last with stout but reduced 

 diapophysis. Caudals without diapophyses, in a supposed species of Plate- 

 carpus, number twenty-seven; and there were at least as man}', judging from 

 the rate of diminution, beyond these. A specimen of Clidastes vymanii lias, 

 according to Marsh, eighty-one with chevron-bones. 



The ribs commence at the axis, which bears a small one. There is no 

 distinct parapophysis ; hence each rib-head is undivided, but is flattened 

 vertically. The anterior may be known by the greater compression of both 

 head and shaft. The rib of the third vertebra has a narrow, convex, articular 

 surface, and is concave on the anterior face. Those of the dorsals are much 

 wider, and with more truncate head. 



The limbs and limb-girdles. 



The limbs in all the members of this order are very small in proportion 

 to the size of the body and tail, and the bones of the scapular and pelvic 

 arches of proportionate small development. 



The scapula is a broad segment of a disk, differing in form from that 

 seen in any other order of the Kcptilia. It only presents facets for the cora- 

 coid and humerus. The coraeoid is a similar bone, but embraces a larger 



1 Professor Marsh (American Journal of Science ami Aits, 1672, p. 454) quotes me as assigning ten 

 cervical vertebr.e with articulated hypapophyses to this species. This I have not done, hut state (Synop- 

 sis of the Extinct Batrachia and Reptiles of North America, p. 221) that it possesses six such vertebra'. 

 Professor Marsh's statement and consequent supposition that he first determined the number of cervical 

 vertebrae in the genus Clidastea arc the result of a misappreheusiou. 



