154 



FOSSIL TURTLES OF NORTH AMKRICA. 



The fibular process rises only to the lower level of the head. The tibial process is broken 

 off. The planes of the two made with each other an angle of more than 90, and there is a 

 broad fossa between them, open below. The ridge from the tibial process runs far down on 

 the shaft. The least diameter of the latter is 12 mm. 



The present species appears to differ from C. repanda in having no traces of sulci between 

 the epidermal scutes, in having the ridge formed from the rib on the under side of the costal 

 more strongly developt and more angular, and apparently in having the hinder peripherals 

 more recurved toward their free margins. To judge from the types, C. ponderosa was con- 

 siderably the larger species. 



In his description of this species Cope mentions a portion of the mandible which had 

 accompanied the other bones. This bone is now at hand. It consists of the right dentary. The 

 tip of the dentary and the hinder portion of the cutting-border are missing. The break 

 between two dentaries appears to have followed the midline. The length of the symphysis 

 was close to 36 mm. and its hinder end extended back to a line joining the mental foramina. 

 The latter are small. From the symphysis the upper surface of the dentary descends slightly 

 outward, then rises considerably to the cutting-border. The lower side of the dentary is 

 flat for a considerable distance on each side of the midline, then rises in a strong curve to 

 the cutting-edge. The thickness at the hinder end of the symphysis is 1 1 mm. The jaw is 

 strongly grooved behind. This dentary resembles that described under O. chelydnnus; but, 

 having the same width, the latter is thicker and heavier. 



Genus LYTOLOMA Cope. 



Lower jaw with broad, flat crushing-surface and long symphysis; the tip not beaked. 



Carapace resembling that of Caretta caretta but less pointed behind. None of the anterior 

 peripherals suturally articulated with the costal plates, rib-pits of most of the peripherals in 

 the hinder half of these bones. The eleventh peripheral with pit for rib of eighth costal. 

 Plastron not well known, but believed to have a narrower connection with the carapace than 

 in Osteopygis. Limbs not well known, the humerus and femur supposed to have about equal 

 development, with tendencies toward the structure of the same parts in Cheloniidae. 



The type of this genus is Lytoloma angusta Cope. This is represented by some peripherals 

 and a lower jaw, all supposed to belong to the same individual. Dr. Wieland has described and 

 figured a considerable portion of a carapace which he referred provisionally to L. angusta, but 

 which is here placed with doubts under L. wielandi. 



A considerable number of species from the Eocene of England and Belgium have been 

 arranged under this genus, after having been assigned variously to Chelone, Euclastes, Puppi- 

 gerus, Glossochelys, Pachyrhynchus, Thalassochelys, and Erquelinnesia. For the discussion of 

 the subject the reader is referred to the original papers. These are cited by Mr. Richard 

 Lydekker in his Catalogue of Fossil Reptilia, part in, page 51. 



It is evident, however, that few, if any, of these species really belong to Lytoloma. Owen's 

 Chelone crassicostata, the palatal view of which is figured by Lydekker (Proc. Zool. Soc. Lond., 

 1889, pi. vi), under the name of Lytoloma crassicostatum, has the choanae pushed backward to 

 the hinder third of the skull, and the palatine bones meet for a considerable distance behind 

 the vomer. In the article accompanying the figure just cited Mr. Lydekker informs us that 

 Dollo's species originally described under the name of Pachyrhynchus gosselett is identical 

 with Owen's Chelone crassicostata. For the genus represented by this species it appears that 

 Dollo's name Erquelinnesia will have to be employed. 



The skull of Owen's Chelone planimentum resembles in general that of his C. crassicostata, 

 but its palate appears not to have been described. Nevertheless, the carapace presents several 

 peculiarities. The neurals have the antero-lateral and the postero-lateral sides equal, the ribs 

 present themselves on the under side of the costals as prominent, narrow, and angular ridges, 

 and the peripherals are much more reduced than in C. crassicostata. It seems probable that 

 we have here a distinct genus, and for this Seeley's name Glossochelys will be available. 



Dr. W. B. Clark has publisht (Johns Hopkins IJniv. Circ. xv, 1895, No. 4; Bull. U.S.Geol. 

 Surv., No. 141, 1896, p. 59) a mention of some fragments of a large carapace found in the 

 Aquia formation in Maryland, which he supposed might belong to Cope's Euclastes. Case 



