No. 3.] 



PELVIS OF THE TESTUDIN^ATA. 



353 



know, the suture between the entopubes is short — in other 

 words, the entopubes are slender ; in the Cryptodira and 

 Trionychia the entopubes are always much expanded. This 

 slenderness of the entopubes, which is also present in the ento- 

 ischia, seems to be produced by the co-ossification of ectopubes 

 and ectoischia with the plastron, for which purpose material of 

 the other elements has been used. In Compsemys of the 

 Amphichelydia, and in Plesiochelys we have a similar condition 

 of the pubis. In the Amphichelydia entopubes are widely 

 separated from the entoischia. In 

 Baena we find the condition of 

 Chelydra, but the tendency is for 

 co-ossification of ectopubes and ec- 

 toischia with the plastron. 



Fig. II. — Emydura Krefftii, Gray. 



E, Epigastroid. 

 M, Mesogastroid. 



It is now very easy to understand the evolution of the pelvis 

 of the Testudinata. The oldest Testudinata possessed a pelvis 

 very much like that seen in Sphenodon, but with the obturator 

 foramen between pubes and ischium ; the gastroid cartilage was 

 continuous ; epi- and hypogastroids were present, and the meso- 

 gastroid separated the entopubes and entoischia. This form 

 was present in the Amphichelydia, and is still preserved in the 

 Chelydridae, Dermatemydidse, Staurotypidae and Platysternidae. 

 The entopubes and entoischia gradually approached and united, 

 a. Cinosternidae, b. Emydidae, Testudinidae ; or became more 

 separated from each other, until they were represented by liga- 

 ment, a. Cheloniidae,^ b. Trionychia. 



1 As I stated above, the marine ancestors of the Cheloniidae must have had a 

 pelvis more or less like the Chelydridae: from such a form the Dermochelyiidse 

 developed. 



