OSTEOLOGY. 



The skull of the Cheloniidas differs in some important respects from that of the 

 Emydidae. In order to illustrate this, figures are here introduced giving upper 

 (plate I, fig. i), lower (plate i, fig. 2), and lateral (plate 2, fig. 1) views of the skull 

 of ' Lepidochelys kempi Garman. These figures were prepared for Dr. George Baur, 

 in 1888, but reverted to the United States Geological Survey, the then director of 

 which, Dr. C. D. Walcott, has permitted them to be used here. No figures of 

 this species have hitherto been publisht. The most interesting feature of the 

 skulls of the sea-turtles is the great extent of the bony roof covering the temporal 

 region. This roof extends from the orbit to behind the plane of the occipital con- 

 dyle. The postfrontal bone, narrow in the emyds, is carried backward nearly to 

 the hinder border of the roof. The squamosal sends upward and inward a plate 

 that meets a horizontal plate from the parietal, forming a parieto-squamosal arch. 



The lower side of the skull is interesting 

 chiefly because of the broadening of the triturat- 

 ing surfaces of the jaws. The palatal plates of 

 the vomer extend backward until they meet 

 similar plates from the palatines. The choanae 

 are thus thrown much farther toward the middle 

 of the skull than in the skull represented by text- 

 figure 4. The crushing surfaces of the lower 

 jaw are correspondingly widened (plate 1, figs. 



3 and 4). In the Thalassemydidas the choanae 

 Fig. S .-C a rettaj*retta. Pelvis from may be pusht much further backward, as may 



be seen by examining the skull of Rhetechelys 

 platyops (Cope). There are no posterior palatine foramina. 



In the Cheloniidae the procoracoid process makes an obtuse angle with the body 

 of the scapula, and there is a distinct neck between the process and the glenoid 

 fossa. The coracoid bone is longer than the scapula and moderately expanded at 

 its free end. These bones are represented by fig. 2 of plate 2. 



The humerus of these sea-turtles is strongly modified from the primitive form. 

 It is much straighter than that of the Emydidae and has become flattened in the 

 plane of the distal end. The head and the radial and ulnar tuberosities have changed 

 positions. The head is turned downward and proximad into the plane of the bone, 

 while the tuberosities are lifted into this plane, each on its proper border of the bone. 

 The radial tuberosity is carried along on the shaft of the bone until it has lost its 

 connection with the head. It becomes divided into two parts, one for the deltoid 

 muscle, the other for the supracoracoid. Fig. 3, plate 2, represents the humerus of 

 Lepidochelys as seen from above; fig. 4, as seen from below. 



Relatively to the humerus, the radius and the ulna are shortened, the ulna 

 more than the radius. In the carpus the radiale remains small, the intermedium 

 and the ulnare are enlarged and flattened, while the centrale is distinct. There are 

 five bones in the distal row, one articulating with each metacarpal. The third and 

 the fourth may be co-ossified. On the ulnar side of the carpus there is a large flat 

 bone assisting to broaden the carpus. It may be regarded as the pisiform. 



The second, third, and fourth digits are greatly elongated, the bones flat- 

 tened, and all are bound together in a mass of muscles and skin to form an undivided 

 oar. The first, and in some cases the second, digit is provided with a claw. 



The pelvis of the Cheloniidae is broad and deprest (fig. 5). The ilia are short; 

 the upper end is slender and turned backward and the axis of the bone is nearly 

 in the plane of the pubes. The latter bones are broad. Between the two, at the 



