NATURAL SCIENCES OF PHILADELPHIA. 235 



transverse than ia any noticed in the British Fossil Reptiles, approaching that 

 figured bj^ him in pi. 3, fig. 22-4; the ball has not the oblique, up-looking 

 profile of that species, but forms a nearly regular arc, with its posterior margin 

 superiorly a little behind its position interiorly. The hypapophysial ridge is 

 considerably interrupted, as in the P. ty phaj us, while P. li tto ral is agrees 

 with the P. toliapicus in having it continuous. The two last named 

 species differ in the development of their hypapophyses ; in the American 

 species both are large, especially the posterior ; in the English, the anterior 

 process is weak or wanting; the ridge connecting the zygapophyses disap- 

 pears in the P. toliapicus and continues in the P. 1 i 1 1 o rali s. The 

 general proportions of the centrum are slender, as in P. toliapicus, and not 

 so stout as4n P. porcatus Owen. 



The diapophyses in the P. h a 1 id an u s are not so pedunculate as in P. ty- 

 p h £6 us, though they are separated above by a notch from the vertical ala 

 which descends from the zj-gapophysis, which I do not find in the P. 1 i 1 1 o ra- 

 ils They approach near the margin of the cup in their transverse extent 

 below. 



The horizontal ridge between the zj-gapophyses is strongly marked, and in 

 the specimen in hand comes off from the anterior vertical ala below the zyga- 

 pophysis, rather than from the plane of that process, as in P. 1 i 1 1 o r a"l i s. 

 The neural (janal is depressed behind, below the margin of the ball, and has 

 an obtuse epapophysis along the median region of its median line. There is 

 no ridge parallel to the hypapophysis. The cup is partially broken, but its 

 transverse diameter appears to have been one-fourth greater than the vertical. 

 The transverse plane of the face of the zygapophysis is transverse. A large 

 part of the neural arch is broken away. 



Lines. 



Length from edge up to convexity of ball 12-75 



Width between anterior zygapophj-ses 13-5 



" of cup 8-4 



Depth " 6-2 



Least width centrum at middle 5-3 



Width neural canal 4- 



Locality. — This serpent was found by my friend 0. B. Kinney in the excava- 

 tions of the Squankum Marl Company, at Squankum, Monmouth Co., N J., a 

 few miles south of Shark River. The horizon is eocene. 



This animal was probably a sea-serpent distantly allied to the Boas, and far 

 exceeding in dimensions those at present inhabiting the Indian Ocean. Its 

 size was similar to that of the very largest of terrestrial serpents of the 

 modern era, and was probably proportioned to a length of twenty feet. 



CHELONIA. 



ADOCUS Cope. 



Emydoid tortoises, in which the rib-heads of the posterior costal bones are 

 represented by rudimental laminte, and the anterior by a crest or truncate 

 ridge in addition. Vertebral scuta narrow; external surfaces smooth or 

 nearly s«. 



Name from A, and a»xoc, rafter (/. «., rib-head). 



This genus, now first characterized, differs from Emys in the absence of cos- 

 tal capitula of the costal plates of the carapace, a feature pointed out by Leidy 

 in the type species. It also possesses a character of Plenrosternum in the pres- 

 ence of a series of marginal dermal plates on the sternal bridge. It belongs to 

 the true Eniydidte, having the eight paired sternal bones instead often of the 

 first-mentioned. The markings of the dermal plates of the plastron ai'e not 

 distinct. Besides the species here described, it includes A. b e a t u s (Emys 

 Leidy), A. f i r m u s (Emys Leidy), A. pr a v u s (Emys Leidy), and A ag i 1 i 3 

 Cope. It represents Emys in our cretaceous, as Osteopygis Cope does Chelydra, 

 and Taphrosphys Cope (type Platemys sulcatus Leidyj dues Hydraspis. 



1868.] 



