488 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



cerned." The presence of "epiphyses" forming nearly the whole 

 of the humerus, their apices separated in the middle of the bone by 

 perforating canals extending through the shaft of the bone, is utterly 

 unlike anything that has been observed in turtles or any other rep- 

 tiles at any stage of then existence. I trust that the myth of epiphy- 

 ses as an evidence of relationship between the turtles and plesiosaurs 

 may not reappear again. ^ 



As to the structure of the scapula, all students of the plesiosaurs 

 are now agreed that the procoracoid does not unite with the scapula, 

 whatever may be the case in the turtles (where it is equally improb- 

 able). The presence of a distinct foramen in the coracoid of many 

 plesiosaurs, or its deep emargination posteriorly, points, I think, to 

 a normal reptilian manner of development of this bone. The tri- 

 radiate structure of the scapula is simply a parallel character, brought 

 about by the same causes which have produced the enormous develop- 

 ment of the coracoids, a structure absolutely lacking in the earlier 

 and simpler nothosaur type, where it would confidently be expected 

 were the orders genetically allied. 



Whatever of resemblance there may be in the form and habits of 

 these two orders of animals has been due solely to parallel evolution, 

 to similar aquatic adaptations. In theu- internal structure they are 

 really remote from each other, and neither could have been derived 

 from the other type, not even in a remotely antecedent stage. The 

 turtles have a stegocrotaphous skull, unlike all other reptiles save the 

 Cotylosauria, Procolophonia, etc. The plesiosaurs have a large tem- 

 poral vacuity, larger indeed than is to be found in any other reptiles 

 of the therocrotaphous (I coin the word) type. Leaving out of 

 account adaptive characters, we have the following most important 

 differences in the structure of the two orders: The turtles lack the 

 lachrymal, postorbital, and transverse bones, all well developed in 

 the plesiosaurs. They have a distinct opisthotic, wanting in the 

 plesiosaurs, and a large quadratojugal, probably wholly wanting in the 

 plesiosaurs. The plesiosaurs have a large pineal foramen, wholl}" 



o See Williston, Field Columbian Mus. Publ. No. 73, p. 73. 



6 In the pigeon " at four days there are two cones of gradually ossifying cartilage, the 

 apices of which are close together in the middle of the bone, at the point where 

 the primary center of ossification occurred, while the bases, quite unossified, form the 

 articular ends. These two cones are ensheathed by a layer of periosteal bone, which 

 of course is thickest opposite the ends of the cones, and thins off as the two extremi- 

 ties are approached. . . . These two cones probably represent the so-called 

 epiphyses of the Plesiosaurus. I have not been able to find that this reptile possessed 

 anything corresponding to true epiphyses." (Parsons, Jour. Anat. and Physiol., 

 XXXIX, 1905, p. 403.) The figure of the bird humerus, given by Parsons, strikingly 

 resembles the ossificatory plan in the plesiosaurs, save that the latter in the early stage 

 has perforating canals through the rudimentary medulla. These observations of Par- 

 sons, seen by me for the fu-st time since the above was in type, effectually dispose of 

 the whole matter of turtle relationships in the manner of ossification of the long bones. 



