No. 1605. ON THREE SPECIES OF SEA-TURTLES—HA Y. 189 
is a thicker bone than in the bastard-turtle, being 34 mm., instead of 
23 mm., where it joins the twelfth peripheral. 
As regards the horny scutes of the carapace of the bastard-turtle, 
we find that they differ not greatly from those of the loggerhead. 
There are nearly always five vertebrals. In the specimen figured by 
Coker there is a small extra one behind the fourth. Irregularities in 
the scutes of the carapace are common in the loggerhead, as has been 
noted by several writers. The length of the sulcus between the mar- 
ginal scutes of the hindermost pair is usually longer in the bastard- 
turtle than in the loggerhead. In the former it is usually about two- 
thirds as long as the fifth vertebral, and the sulcus between the two 
marginals mentioned and the vertebral runs in a straight line across 
the second suprapyga!. In the loggerhead the sulcus between the 
marginals in question may be only about one-half as long as the fifth 
vertebral, and the suleus between the marginals and the vertebral 
makes an angle backward at the midline. However, the large log- 
gerhead, No. 29013, does not differ in the respects named from the 
bastard-turtles. 
The plastron of the bastard-turtle resembles closely that of the log- 
gerhead. The large individual mentioned above, No. 29323 (Plate 
VI, fig. 2), has the anterior and the posterior lobes broader and more 
rounded than those of the loggerhead, but such differences do not 
seem to exist in the smaller specimens of the two species. In the large 
individual the fontanels usually found on each side between the outer 
end of the hyoplastron and of the hypoplastron are filled up. The 
median fontanels also are much reduced. In this specimen the plas- 
tron is 515 mm. long. The anterior lobe is 230 mm. wide at the base; 
the posterior 220 mm. The bridge has a width of 165 mm., of which 
the hyoplastron occupies 90 mm. 
The scutes of the plastron of the bastard-turtle are, in general, like 
those of the loggerhead. Both have small intergulars. As already 
stated, there are, on each bridge, four inframarginals, of which the 
hindermost is the shortest, fore and aft (Plate VI, fig. 2). In such 
loggerheads as the writer has examined there are only three inframar- 
ginals and the hindermost is the largest. 
Striking differences are found when we compare skulls of the bas- 
tard-turtle with those of the loggerhead. For comparison there are 
presented below three sets of measurements, one from the skull of 
the large specimen of the bastard-turtle, No. 29323 (Plate VII, fig. 2; 
Plate VIII, fig. 2; Plate IX, fig. 1; Plate XI, fig. 4), another from the 
loggerhead skull No. 13822, and a third from the loggerhead skull 
No. 29206. The length of the skull of the bastard-turtle, from the 
snout to the occipital condyle (cranial axis), 1s 147 mm.; that of No. 
13822 is 182 mm.; that of No. 29206 is 175 mm. In the table there are 
presented under each of these specimens two columns of figures. In 
