No. I.] ARRANGEMENT OF THE SAUROPSIDA. 99 



veloped, they are mainly connected with the posterior part of 

 the vertebrae. 



Another proof of the affinity of the Testudinata and Saurop- 

 terygia is given by Parker.^ 



He says : " There is one thing of great importance to be 

 noted in the development of the Turtle, and that is the number 

 of its body-segments at various stages, their rapid increase at 

 first, and then the suppression or extinction of several after- 

 wards. 



" In embryos a little more than a quarter of an inch in length 

 there are about 27 muscle-plates or somatomes. 



" In embryos ranging from 6j4 to 9 lines there are 5 1 of 

 these divisions of the body visible externally. 



"Now, in the adult I can only find 41 developed vertebrae, 

 viz.: 8 cerv., 10 dorsals, 2 sacr., 21 caud., — 41 in all. 



"But in the third and fourth stages there are at least 15 

 somatomes in the cervical region; in the dorso-lumbo-sacral, 12 

 (as in the adult), and 24 in the caudal, — 51 in all. Thus we 

 miss in the adult 7 in the cervical and 3 in the caudal, — 10 in 

 all. 



" This free suppression of segments suggests a great secular 

 modification by shortening of a form not unlike a Plesiosaur." 



If it seems from the foregoing that the Testudinata are more 

 or less related to the Sauropterygia, the question arises, which 

 is the group of Reptiles ancestral to both? It is none of the 

 known groups, and we can only admit that we do not know any- 

 thing of the ancestors of the Testudinata and Sauropterygia ; 

 that it was a group allied to the Rhynchocephalia is probable. 

 The Testudinata have an epipterygoid (columella), and it may 

 be that the plastron of Testudinata was developed from or on 

 abdominal ribs of a form like Sphenodon. 



Rhynchocephalia, Lacertilia, Pythonomorpha, Ophidia. 



Prof Cope puts the Rhynchocephalia in one group, with the 

 Testudinata and Sauropterygia. I do not find that natural. I 

 find it very much more natural to combine the Rhynchocephalia 

 with the Lacertilia, Pythonomorpha, and Ophidia. 



The Rhynchocephalia are the most generalized of these ; 



' Parker, W. K. Report on the Development of the Green Turtle (Chelone 

 viridis Schneid). The Voyage of H. M.S. Challenger. Zool., Vol. i., p. 47. 



