284 FOSSIL TURTLES OF NORTH AMERICA. 



35 mm. The first has a length of 45 mm. In form the vertebrals resemble those of Staurotypus 

 salvinii. Along the hinder ends of each of the lateral borders of the three anterior vertebrals 

 there is a very deeply imprest groove. In the case of the first and second vertebrals these 

 grooves extend backward on that neural bone which is crost by the hinder border of each ver- 

 tebral respectively. The grooves along the third vertebral scute run backwards on the prox- 

 imal ends of the costals of the fifth pair. 



The marginal scutes rise relatively little above the free borders of the shell, the second 

 having a fore-and-aft extent of only 13 mm.; the tenth, of only 15 mm. The costal scutes are 

 therefore relatively broad. 



The plastron (fig. 356) has a total length of 163 mm. Where narrowest, the bridge has a 

 width of only 43 mm. The axillary' and inguinal notches are very narrow. The plastron was 

 united with the carapace bv a close suture, but there are no buttresses rising from the plastron. 

 The anterior lobe has a length of 52 mm. and a width of 80 mm. at the base. It is broadly 

 rounded in front and somewhat repand. The border is acute. The entoplastron is broadly- 

 oval, 29 mm. long and 27 mm. wide. The hinder lobe has a length of 75 mm., and a basal 

 width of 62 mm., and is deeply notcht behind. The free border is acute, but the thickness 

 increases above, so that where the soft skin began the thickness was 6 mm. In the middle of 

 the upper surface of each xiphiplastron there is a rather deep, smooth impression, which was 

 probably for the lateral process of the pubis. 



According to Riitimeyer (Denkschr. schweiz. naturf. Gesellsch., xxv, 1873, p. 152) 

 Dermatemys mawii possesses on each xiphiplastron a depression (Bandgrube) for the insertion 

 of the lateral process of the pubis. 



The antero-posterior extent of the epiplastra is 35 mm.; that of the hyoplastra, 41 mm.; 

 that of the hypoplastic, 30 mm.; that of the xiphiplastra, 57 mm. 



Besides the inframarginal scutes, there are only 5 pairs on the plastron of this species. 

 Of the inframarginals there are 2 on each bridge a small anterior and a large posterior. 



It is difficult to interpret the anterior plastral scutes. Posteriorly we find anals and 

 femorals, in the usual positions. In front of the sulcus bounding the latter anteriorly there 

 is not a trace of a transverse sulcus until we reach the anterior end of the entoplastron. Occu- 

 pying the front of the anterior lobe are 2 pairs of scutes, which look like intergulars and gulars; 

 altho it is not certain that the former are not consolidated into a single scute. It is evident that 

 there has occurred either a fusion of 2 pairs of scutes or an extirpation of one pair. If the most 

 anterior pair are intergulars, we must account for the absence of 2 pairs of scutes. In Der- 

 matemys the humero-pectoral sulcus has moved forward to near the anterior end of the hyo- 

 plastron. In Adocus pectoralis this sulcus has lain partly on the epiplastron. It appears 

 probable, therefore, that in Xenochelys the sulcus named has moved far forward; that is, 

 to the middle of the epiplastron. If this is the case, we have here gulars and humerals, instead 

 of intergulars and gulars. We have then to suppose either that the pectorals and the abdom- 

 inals have fused, without a trace of the sulcus between them, or that the pectorals have 

 extended backward so as to suppress the abdominals. In T estudo osborniana the pectorals 

 have been nearly supprest by the forward expansion of the abdominals. The writer accepts 

 the view that in Xenochelys we have present the gulars, humerals, pectorals, femorals, and 

 anals. The pectorals have an antero-posterior extent of 68 mm. at the midline; the femorals 

 a similar extent of 32 mm.; the xiphiplastrals, of 37 mm. 



It may be noted here that the specimen of Dermatemys maivn figured by Dr. Boulenger 

 (Catalogue of Chelonians, p. 28) possesses only 7 pairs of costal plates. Amie Bienz (Rev. 

 Suisse Zool. et Ann. Mus. d'Hist. Nat. Geneve, in, p. 61) states that the species has 8 pairs of 

 costals. The same statement is made by Dr. Riitimeyer (loc. cit. ). 



Family EMYDID-ffi Gray. 



Cryptodire turtles distinguisht by the following characters: Shell covered with epidermal 

 scutes. Peripherals articulated to costals by close sutures and by gomphosis of rib-ends. 

 Neurals in lull series. Bridges broad, usually sutured to peripherals; in rare cases ligament- 

 ously attacht. Plastron broad, composed of 9 bones, the mesoplastron never present. No 

 intergulars and no inframarginals, except axillary and inguinal. Procoracoid process forming 



