224 FOSSIL TURTLES OF NORTH AMERICA. 
So far as the writer can determine, there is no good reason for separating the fossil genera 
that have been arranged under the name Adocrde from the living dermatemyds. The name 
Dermatemyde was employed by Gray in 1870, apparently a Sheet time before Cope pro- 
posed the name Adocide, and ought, under the form Dernzatemydid@, to be used for the family. 
It is difficult to frame a definition of the family. Our knowledge of the few living forms 
is not complete. Of the great mass of the fossil genera we are acquainted with little more 
than the shells, and often with only small portions of these. Of no fossil genus have we the 
skull, except that of Baptemys. The limbs and feet and the caudal vertebra are unknown. 
In the shells there is a great variety of structure. Perhaps no other family furnishes so many 
deviations from what is regarded as the normal condition in turtles. 
Usually in the members of this family some of the hinder neurals are aborted, a condition 
that permits one or more pairs of the hinder costals to meet their fellows in the midline. In 
Baptemys, however, there is a full series of neurals. In the living genera, Staurotypus and 
Claudius, he nuchal bone has long costiform processes, and the possession of these has been 
regarded as a characteristic of the family; but these processes are absent in Dermatemys ; 
while i in Adocus and Xenochelys, and perhaps others, they are short; in Anosteira they are 
absent. The plastral lobes are in nearly all cases shortened and often narrowed. In the 
living Dermatemys (fig. 286) the lobes are quite 
well developt. In nearly all forms the plastron 
is suturally articulated with the carapace; but 
in living Claudius the union is ligamentous. 
In some of the fossil genera the sutures are 
coarse, forming a transition from the ligamen- 
tous connection to the closely knit sutures. 
In Adocus and Baptemys axillary and inguinal 
buttresses rise to the costals, or nearly so. In 
probably all genera, except Basilemys, there 
is a series of inframarginal scutes crossing the 
bridge. In Xenochel ys and (penn the 
number is reduced to two. In probably all 
genera there is some deviation in the arrange- 
ment of the scutes of the anterior lobe from the 
arrangement seen in such a primitive turtle as 
Baéna. In Adocus and some others, this pro- 
ceeds no further than the great development of 
the intergulars, by virtue ot which the gulars 
are greatly reduced and pushed far from each 
other. If this should in any cases have proceeded to the entire suppression of the gulars, 
the usurping intergulars would be mistaken for the abolisht scutes. Undoubtedly, in some 
cases, there has occurred either a coalescence or a suppression of scutes. In Baptemys 
wyomingensts there are only 5 pairs on the plastron, excepting the inframarginals. Two pairs 
occupy the area covered in Adocus by the intergulars, gulars, humerals, and_pectorals. 
The pectorals appear to have advanct so as partly to cover the epiplastrals. Three pairs of 
scutes ought to be found in front of this; but there is only one pair. In B. tricarinata, there 
are apparently distinct evidences of a sulcus crossing the front of the entoplastron and the 
middle of each epiplastron. This probably bounds the humerals in front.. It seems probable 
that the area in front of this sulcus is occupied by the intergulars and that the gulars have 
been extirpated. 
The plastral scutes of 4gomphus appear to be arranged like those of Baptemys. 
In Xenochelys we find the modifications of the plastral scutes to have gone still further. 
On each bridge there are only 2 scutes. What we must regard as the intergulars have coalesct 
into a single scute. This is followed by a scute on each side which does not come to the mid- 
line. T He whole area extending from these to the femoral scutes is occupied by a single pair 
of scutes. The pair of scutes ‘following the intergular may be gulars, but it appears more 
probable that the pectorals have advance still furiier forward ‘fan in Baptemys and have 
Fic. 286.—Dermatemys mawt. Carapace and 
plastron. After Boulenger. 
infm 1, etc., inframarginal scutes. 
