50 THE VOYAGE OF H.M.S. CHALLENGER. 



General Conclusions. 



The Turtle agrees with the Lizards in having a large orbito-nasal septum and an epi- 

 pterygoid, and in the mode of ossification of the occipital arch and auditory capsules ; it 

 differs from them in having the alisphenoid quite aborted, and the opisthotic permanently 

 distinct. 



It agrees with the Chameeleon in having a single vomer, but differs from it in having 

 an epipterygoid, a tympanic cavity, a functional columella, a rudimentary cochlea, and 

 a fenestra rotunda ;. in which characters it agrees with the typical Lizards. 



It agrees with Hatteria and the Crocodile in having a quadrato-jugal, and in this 

 character differs from the other Lizards and Snakes. Although forming in the adult 

 condition so great a contrast to the Snakes in their outward form, it agrees with them and 

 differs from other reptiles in having neither sternum nor sternal ribs, the whole plastron 

 and much of the carapace being formed of membrane bones. 



The Turtles, like the Batrachia, are remarkable for the fewness of their investing 

 bones ; the nasals and prefrontals are ossified as one tract, and there are no super-orbitals, 

 no second temporal bone, and no splenials. 



One of the most remarkable things in the early embryo is the large number of soma- 

 tomes, in the neck especially, and also in the tail, as compared with what is seen in the 

 intercalary bony segments (vertebrse) of the adult ; thus, the embryo suggests an ancestry 

 having a longer neck and tail than the existing forms. As some of the Cretaceous Chelonia 

 certainly possessed teeth, and as a few forms, both fossil and existing, have the nasal 

 bones distinct from the prefrontals, it is evident that the modern Chelonia are forms that 

 have become separated from their nearest reptilian relations by specialisation. A long 

 necked ancestry with a feebly-developed carapace, and many feeble bones of the plastron 

 arranged triserially, would bring us very near to the Plesiosaurs. The great and close 

 conformity of the Turtles, even now, to the Lacertilia, suggests a common parentage.^ 



' The magnifloent skeleton of the Leathery Turtle (Sphargis coriacea), recently added to the treasures in the British 

 Museum, has its ribs distinct from each other, as in yoiang embryos of the ordinary kind, and as in the extinct Plesio- 

 saurs. 



