116 THE WASATCH AND BKIDGEK FAUNiB. 



AXESTUS Cope. 



i»roceed. Amer. Pbilos. Soc, 1872 p. idi, (publiNLed July 29). Annual Report U. S. Gool. Surv. 



Terrs., 18/2 (lb7:!), p. 615. 



This is a genus of Trionychidae which is represented by a species not 

 fully known. The type specimen is represented by bones of the limbs 

 and various vertebrae, with the post-abdominal bone of the left side. 



The general characters are those of Trionyx. The scapula is elongate, 

 the procoracoid long and narrow, and the coracoid of medium width. The 

 humerus is sigmoid, with widely separated tuberosities, and flattened extrem- 

 ity, with marginal groove. The femur is also curved, but less strongly than 

 the humerus, and has a median anterior low angular ridge. The claws are 

 large, some curved, and some entirely straight. The cervical vertebrae are 

 relatively large and elongate. The two sacrals are free from the carapace 

 above, have broad articular surfaces for diapophyses, and flattened centra. 

 The caudals are procoelian, and have short diapophyses. The post-abdomi- 

 nal bone has the form seen in existing Trionyx. It presents two dentate 

 processes forwards for the hyposternal, and two inwards to its mate in front. 

 It is prolonged backwards and inwards into a flat process. It is especially 

 distinguished by its tenuity, and the entire absence of the superficial sculp- 

 ture of Trionyx. The usual dense layer is present, but is quite thin, and 

 exhibits the peculiar decussating pattern of lines of deposition character- 

 istic of the same layer of the dermal scuta of Crocodilin. No portions were 

 obtained which can with certainty be referred to the carapace. The ilium is 

 short, stout, and recurved, and the pubis is largely expanded. 



AxESTUs BYssiNus Cope. 

 Loc. cit. 



Plate XV, figs. 1-12. 



The procoracoid and scapula are of equal lengths, and the coracoid is 

 much dilated distally. 



The portions of plastron preserved are thin for the size of the animal, 

 and all the bones are especially dense and smooth. The post-abdominal has 

 the free margins acute and serrulate. There is an external, gently convex 

 edge, with a long process extending backwards; and one long narrow one 

 inwards. The dense layer is marked with decussating lines of osseous 



