186 PROCEEDINGS OF THE NATIONAL MUSEUM. vou. xxx1v. 
no wear in the large specimen mentioned. In a loggerhead, No. 
29372, the horny ridges grow broader forward and join along the 
midline, there being hardly any notch between them. A smaller speci- 
men shows similar ridges. In the older individuals of the loggerhead 
the ridges are often strongly worn, as is seen in No. 29013 (Plate 
VIII, fig. 4). In the smaller specimens of the bastard-turtle the ante- 
rior ends of the ridges may not be so well defined as in the larger ones. 
On the buccal surface of the lower horny jaw-sheath there is, in 
the bastard-turtle, a broad groove, bounded in front and at the sides, 
by the cutting edges of the jaw, posteriorly by a sharp ridge which, 
starting from a prominent triangular tooth, runs backward and out- 
ward on each side (Plate VII, fig. 3). Its hinder slope is very short. 
In the loggerhead (Plate VIII, fig. 3) there is a corresponding ridge, 
but the median tooth is wanting, the groove in front is not so deep, 
and the hinder slope is longer. 
It is believed that specimens of the two species may be distin- 
guished by differences in the form of the lateral borders of the cara- 
pace. If we will examine this border below the third costal scute 
(counting the small anterior one) of the loggerhead we shall find that 
the upper face makes about a right angle with the lower, or outer, 
face and that the latter is quite narrow, about one-third the length 
of the marginal scutes of that region. In the bastard-turtle the upper 
and the lower faces make an angle of about 45° between them and 
the width of the lower face is from one-half to two-thirds the length 
of the neighboring marginal scutes. 
It appears, further, that the bastard-turtle has four inframarginal 
scutes on each bridge (Plate VI, fig. 2), while the lecahendl has 
only three. In the figure cited these scutes show most distinctly on 
the left side. 
Mention has been made above of the relation between the length 
and the width of a specimen of the bastard-turtle. Another individ- 
ual, No. 29015, has the carapace 278 mm. long and as many milli- 
meters wide. The largest individual in the U. S. National Museum, 
No. 29323 (Plate VI), has the carapace 680 mm. long and 664 mm. 
wide. One of Garman’s specimens had the length and the width 
nearly equal, about 652 mm. The other was 703 mm. long and 728 
mm. wide. 
The carapace of the bastard-turtle appears to differ constantly from 
that of the loggerhead in having several supernumerary neural bones. 
In the latter species there are normally 7 or 8. No. 15259 has an 
imperfect extra neural behind the first, while No. 290138 has a com- 
plete one in the same place. In the bastard-turtle the number of 
neurals may vary from 11 to 14. Doctor Baur, as cited, noted the 
presence of 13 and 14 neurals. No. 29015 has 13 and the specimen 
in the American Museum of Natural History has the same number. 
