EMYDID. 347 
The nuchal bone here described has a median length of 70 mm. ‘The anterior border has 
a width of 37 mm. The extent between the lateral angles is 77 mm. The hinder border 
measures 17 mm. The anterior border is acute. From this the bone thickens backward on 
the under side for a distance of 40 mm. Here the thickness is 20 mm. On the midline the 
greatest thickness is 17 mm. The excavation for the first neural is narrow and the bone is here 
€ mm. thick. 
The nuchal scute is 32 mm. long, 5 mm. wide in front, 17 mm. wide behind. The fore- 
and-aft extent of the first marginals is 44 mm. The front of the first vertebral scute is 51 mm. 
wide. Backward it narrows slightly, then again expands. It extends backward on the bone 
a distance of 38 mm. ‘The lateral angles are occupied by portions of the first costal scutes. 
The sculpture consists of more or fess continuous ridges of quite uniform height, separated 
by sharp grooves. Usually there are 5 or 6 of these ridges i in a line 10 mm. long. On the 
nuchal scute area these ridges are parallel with the riidline, On the area of the first marginal 
they run outward and forward, making an angle of about 25° with the midline. On the area 
covered by the first vertebral scute the ridges are nearly parallel with the midline, those along 
the lateral borders of the scute diverging somewhat. The ridges of the areas of the costal 
scutes are the most prominent, and they make an angle of about 45 degrees with the midline. 
Specifically this species is very different from D. réticulaia. In the latter the first vertebral 
scute excludes wholly the costal scutes from the nuchal bone. This bone ts far thinner than in 
» floridana. 
No other bones in the collection can be referred with certainty to this species. In the 
collection there is the front two-thirds of the right first costal plate of a turtle that is provision- 
ally placed here (plate 54, fig. 2; text-hg. 
x '\ re 450). It fits quite accurately against the 
\ : ia a postero-lateral border of the type bone and 
\. \ “agrees with it in sculpture and thickness. 
Furthermore, the costo-vertebral sulcus coin- 
cides with that of the nuchal. The distal 
end of the bone is thickened and on the inner 
surface excavated for the axillary buttress. 
A peripheral, the right second, may 
belong to this species. Fig. 450 represents 
the type nuchal, the first costal mentioned 
above, and this peripheral, placed in their 
proper positions with reference to one 
another. The height of the peripheral i is 
Fic. 450.—Detrochelys floridana. Nuchal, first and only 34 igeboues but when we examine the 
second peripherals, and part of first costal. ><}, Same bone in D. reticulata we find that it too 
Partly restored. is reduced in the line from the free border 
: to the upper border. This is a result of the 
narrowing of the carapace. The first costal scute descends on the bone a distance of 26 mm. 
The sculpture on its area is directed downward. On the area of the second marginal scute 
the ridges run at nearly right angles with the free border. On the area of the succeeding 
scute they are directed dew aor and strongly backward. 
In the Jarman collection is the portion of a left xiphiplastron extending backward from 
the femoro-anal sulcus. The lower surface is ridged and grooved like the type nuchal, the 
ridges being directed parallel with the midline. ae hinder border of the plastron was slightly 
notcht, as in D. reticulata. At the midline the bone is from 5 mm. to 7 mm. thick. The 
plastron had a length of about 290 mm. The bone greatly resembles the corresponding part 
of D. reticulata. 
' 
Genus TRACHEMYS Agassiz. 
Shell varying from deprest to rather elevated. Usually at least traces of a dorsal keel. 
Neural plates hexagonal, with broad end in front. Carapace sometimes smooth, but more 
usually with priktes and grooves; occasionally elaborately sculptured. Hinder border of 
carapace usually more or fess serrated. Plastron with a distinct lip in front and a shallow 
