36 



THE EXTINCT BATRAOIIIA, REPTILIA 



has not attained such huge dimensions as some of the latter. These fragments do not 

 throw much light on the structure of the pelvic arch. 



The structure of the hones is, like that in the order generally, of the coarsest descrip- 

 tion. There are no medullary cavities, but the medullary cells arc large, and extended 

 everywhere in the direction of the axis of each bone. 



The characters which separate this genus from Plcsiosaurus may be derived from the 

 preceding as follows : 



First; the deeply biconcave, and very short vertebral centra. 



Second; the tibia broader than long, resembling those of Ichthyosaurus. 



Third; the coalescence and depression of some of the cervicals. 



Fourth ; the continuity of the neural arches. 



Fifth ; the continuity of the diapophyses of the caudals. 



The only genus with which this genus compares nearly, is the Thaumatosaurus of 

 Meyer. This is known but by a few fragments, and of these, but few are present in the 

 Kansas animal. The character on which I rely at present to distinguish them, is the 

 much less concavity of the dorsal vertebra; in Thaumatosaurus. This is however, not 

 entirely satisfactory. Thaumatosaurus oolithicus Meyer is from the lower oolite of South 

 Germany. 



The hones are thoroughly mineralized, and the adherent matrix is a, light yellow 

 chalky limestone, similar to that which yielded tin; fine fragments of the Macrosaurus 

 proriger. This, Dr. Leconte informs me, is probably Meek and llayden's upper Cretaceous 

 No. 3, and is a higher horizon than that near Fort Wallace from which Dr. Turner 

 procured the Elasmosaurus platyurus. The specimens were all taken out under the 

 direction of W. E. Webb, of Topeka, from the same spot; from every point of view there 

 is reason to believe that they belong to the same animal. 



POLYCOTYLUS LATIPINNIS, Uope. 



The anterior dorsal vertebra have the centra slightly compressed or vertically oval, while the posterior are more 

 rounded. The anterior caudals appear to have been round or nearly so; they are somewhat distorted by pressure. 

 Tin; sides of the centrum are slighly concave in (lie longitudinal direction; below, there is no carina, but at least two 

 venous foramina. There is another large foramen on the side, of the centrum, usually not far from the, neural arch ; 

 there: .-in- usually other smaller foramina below this. The bases of the diapophyses are longitudinally grooved 

 behind, and separate a, concavity of the arch in front of them from one behind. In the most median, the most 

 elevated diapophysis stands about equally on the neurapophysis and the neural spine above it. The diapophysis 

 are vertically oompressed, and the costal articulation of the only one preserved, is in the same plane. The margins 



of the externa] surfaces are, not coarsely striate as in many Sauropterygia. The venous foramina of (he dislal 



coossified cer\ Icals are in pairs, and of a large size. I n the proximal caudals the diapophyses arc above the middle of 

 the sides of the centra, [n one the basis of a chevron is preserved. It is cylindric and striate. The zygapophysis 



