IOO H. H. NEWMAN. 



and it is natural to look for primitive characters in this family, 

 especially in the less specialized regions of the body. 



A careful study of the portion of the body posterior to the 

 carapace, which for convenience may be called the "tail-trunk," 

 is fruitful of suggestions. A preparation of the bony structures 

 of this region was made from a very large specimen (Fig. 58) 

 measuring nearly three feet from snout to tip of tail, having a 

 carapace sixteen inches long and a tail-trunk fifteen inches long. 

 The preparation shows the following structures : 



There are 33 vertebrae ranging in size from very large bones 

 of nearly a cubic inch displacement to very minute ossicles at the 

 tip of the tail. The first five vertebrae "are beneath the carapace 

 and have their dorsal processes in close contact with a longitu- 

 dinal bony ridge that traverses the last three plates of the neural 

 row of the carapace. These five vertebrae have definite flattened 

 ribs that project laterally about at right angles to the axis of the 

 vertebral column and remind one of the flattened ribs in the cara- 

 pace of Dernwclielys. The first and second of these ribs are very 

 large and articulate by means of enlarged heads with the proxi- 

 mal ends of the ileum. These specialized vertebrae and ribs form 

 the sacrum (Fig. 58, I and 2). 



Surmounting the dorsal processes of the eighth to the fifteenth 

 vertebra is a row of six large bony tubercles ( /. I to 6) that 

 have no reference to individual vertebras. The dorsal processes 

 of the latter are not the centers of ossification for the tubercles 

 and there is no articulation or fusion between the two series of 

 structures. Posterior to the sixth bony tubercle are fourteen 

 tubercles (j. 1 14), with either membraneous cores or no cores 

 at all, ranging in size from structures almost as large as the sixth 

 bony tubercle to extremely small scales with dorsal ridges. An- 

 terior to the first bony tubercle are three small soft tubercles (x) 

 occurring at intervals of about half an inch, and anterior to these 

 we find the two procaudal (//. i and 2) and the single pygal 

 plate (/) of the carapace, overlying the first four vertebrae. We 

 have then the following heterogeneous series of structures : two 

 procaudals, one pygal, three small soft tubercles, six large tuber- 

 cles with bony cores and finally a graduated series of 14 tuber- 

 cles merging into ridged scales. It seems reasonable to suppose 



