TRIONYCHID^E. 513 



The sculpture of the carapace is coarse, and consists of deep pits of rather regular size, 

 surrounded by walls which are as wide as the pits themselves. The figures of plate 97 show 

 the general character of the ornamentation. The ridges which run across the costal plates are 

 strongly developt, while the connecting ridges are less prominent. There are four rows of pits 

 in about 15 mm. The sides of the pits rise more abruptly and the summits of the ridges are 

 broader and more rounded than in A. halophila. On the proximal ends of the costal plates, 

 as shown by fig. 2. plate 97, the pits are arranged irregularly and vary much in size. 



The pits of the fragments of the plastron are smaller than those of the carapace and not 

 so deep. 



Until more of the carapace of this species shall have been secured, we shall be uncertain 

 as to its generic position. 



Amyda? halophila (Cope). 

 Plate 96, figs. 4, 5. 



Trionyx halophilus, COPE, Proc. Acad. Nat. Sci. Phila. 1869, p. 12; Cook's Report Geol. New Jersey, 

 1868 (1869), Append. B, p. 735; Trans. Amer. Philos. Soc., xiv, 1869, p. 151, plate vii, fig. 15; 

 Vert. Cret. Form. West, 1875, p. 261. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 454. 



This species is said by Professor Cope to have been founded on numerous portions of the 

 carapace and plastron, some from near Summit Bridge, New Castle County, Delaware, and 

 some from Camden County, New Jersey. Whether or not these represented more than two 

 individuals we are not informed. In the Cope collection of reptiles in the American Museum 

 of Natural History there is a lot of bones, No. 1476, consisting of about 35 fragments of 

 costals, neurals, and at least I piece of the plastron. With these is found Cope's label, as 

 follows: "Trionyx halophilus Cope. Type spec. Pits of Benj. Biggs, Summit Bridge, New 

 Castle County, Del., 1867." In George H. Cook's Geology of New Jersey, p. 734, Cope 

 states that in New Jersey this species comes from the lower marl bed of the Cretaceous. 



It is difficult to determine what meaning to attach to Cope's use of the terms "No. I," 

 "No. 2, " etc., in his table of measurements on page 1 52, of the Transactions American Philo- 

 sophical Society, as cited above. It may mean that he had portions of 5 individuals, which is 

 the more probable conclusion. He speaks of having one costal plate which retained a portion 

 of the head of one rib, and in the measurements he mentions it as "costal plate No. I." This 

 fragment is yet in the collection, and is the one figured by him; but it is not the first costal. 

 His "centrum vertebra No. 2" is also present, but the shortness of the neural plate attacht to 

 it, only 27 mm., appears to indicate that it is one of the posterior neurals. 



This species was a rather large one, the length of the carapace of the individual, or indi- 

 viduals, represented by the remains before us, having probably been about 275 mm. The 

 larger fragments of costal plates indicate that the carapace was considerably archt from side 

 to side. The shell was quite thick and heavy; and the ribs stood out prominently on the under 

 side of the distal ends of the costal plates. The thickness at the sutural border, at the outer 

 end of one costal is 8 mm., while thru the rib it is 15 mm. The width of the costal at the 

 outer end was at least 56 mm. On plate 96, fig. 4, is represented of the natural size a neural 

 plate and a portion of a costal which belonged together. They are the same bones that Cope 

 has figured. The greatest length of the neural is 37 mm.; the greatest width, 35 mm.; the 

 thickness, 8 mm. The length of the fragment of costal is 60 mm.; its width, 38 mm.; its thick- 

 ness, at the costal margin, 7 mm.; at the middle of the width, 9 mm. The inner surface dis- 

 plays the base of the rib-head. Cope states that his figure is half the natural size but, while 

 the length of the figure of the piece of costal is slightly more than half the size of the original, 

 the dimensions of the other portions are three-fifths of their natural size. Fig. 5 of plate 96 

 represents a portion from the middle of the length of a costal plate. The right and left sides 

 of the figure are the sutural borders. 



The neural plate which surmounts the centrum spoken of by Cope as "No. 2" is damaged 

 somewhat, but it has had a length, in the midline, of 25 mm. and a width of 28 mm. The pos- 

 terior border is convex, the anterior concave. 



The slight evidence afforded by one costal indicates that the free border was rounded 

 off in section. The rib projected somewhat beyond the edge of the plate. 

 33 



