l 2 8 E. C. CASE 



clearly distinct from the Cotylosauria, the points of ordinal difference 

 being the exposure of the quadrate to the lateral surface of the skull, 

 the meatus auditus externus forming a third pair of openings in 

 the skull roof, and the peculiarities of the palate cited below. The 

 presence of a more or less well-developed carapace is perhaps defini- 

 tive, but, as it occurs in many Permo-triassic reptiles, and even in 

 Amphibia, Dissorophus, it is not fundamental. Cope included 

 in the Diadectidae (Cope, 1896 1 ) Diadectes, Empedias, Chilonyx, 

 Bolbodon, and Phanerosaurus, which he defined as Cotylosauria 

 "with hyposphen-hypantrum vertebral articulation, and teeth 

 with robust, molariform crowns transverse to the jaws" (Cope, 1898). 

 Of these, Chilonyx and Phanerosaurus must be excluded from 

 the Chelydosauria, as the quadrate is covered on the lateral surface 

 by the squamosal and prosquamosal bones, and there is no external 

 meatus perforating the skull wall; Bolbodon is a very uncertain 

 form, the condition of the specimen rendering an accurate judg- 

 ment impossible. 



DESCRIPTION OF SPECIMEN NO. IO75 



The total length of the specimen as it lies is about i.o8 m . This 

 is nearly the natural length, as only a few inches of the tail seem 

 missing. The animal either died in the soft mud in which it is 

 preserved, or was entombed therein immediately after death, as 

 there is no trace of movement by currents or the attacks of predatory 

 animals. The fine mud penetrated all parts of the skeleton, pre- 

 serving the bones in their natural position almost perfectly. Unfortu- 

 nately, the distal portion of all the limbs have been lost, so that 

 only the proximal halves of the radius and ulna, tibia, and fibula 

 have been preserved. As shown in the photograph (Fig. i), the 

 head is somewhat erect. This is not entirely the accident of fossili- 

 zation, for, as pointed out by Boulenger, the Cotylosaurians had 

 no neck to speak of, and the position of the head is partly the result 

 of its close attachment to the body. The thoracic and pelvic girdles, 

 because of their peculiar solidity, have been preserved undisturbed, 

 with the exception that the scapula-coracoids of the two sides have 

 been pressed together about i cm , giving a false appearance of 

 overlapping. The vertebra? are in the normal position above the 



