1887.] 



Ceratoehelys sthenurus. 



233-' 



were long since rightly determined to be Chelonian by Mr. Davis, 

 and set aside as such. 



Several of the most important of these numerous and, in general, 

 very fragmentary bones were originally found imbedded close together 

 in the same block of sandstone. They consist of a great part 

 of a pelvis, a caudal vertebra, and an imperfect skull. Of the 

 pelvis, a right ischium and a pubis are imbedded in the rock, while 

 an imperfect right ilium, which fits well on to the ischium, is 

 separate ; all these bones are unmistakably Chelonian. The caudal 

 vertebra has remarkable peculiarities. It resembles an ordinary 

 Chelonian caudal vertebra from the anterior half of the tail, in its 

 general characters ; but it is strongly opisthoccelous, the centrum 

 having a deep cup behind and a correspondingly curved articular head 

 in front. From the posterior part of the ventral face, two stout pro- 

 cesses diverge, and present terminal rounded facets for the rami of the 

 large chevron bone which must have articulated with them. Asa 

 general rule, the caudal vertebras of Chelonia are proccelous — but 

 Chelydra and Gypochelys (perhaps also Staurotypus and Platy sternum) 

 form well known exceptions,* in so far as the vertebrse behind the 3rd 

 or 4th are strongly opisthoccelous. In fact, the vertebra in question 

 closely resembles the 6th or 7th of Chelydra or of Gypochelys (see 

 figs. 1 and 2). In the first, however, the transverse processes are 



Fig. 1. 



Caudal vertebra of Ceratoehelys. N, platform on the neural arch ; pz, pre 

 zygapophysis mutilated ; tr, broken transverse process ; Chv', processes for the 

 chevron bone ; Chv, chevron bone. 



* The opisthoccelous character of most of the caudal vertebrae of Chelydra was 

 first pointed out by Von Meyer in his description of the (Eningen Chelydra. Baur 

 (" Osteologische Notizen/' 'Zool. Anzeiger,' No. 238, 1886) has gone fully into the 



