I \M DID.l-. 



347 



The nuchal hone here described has a median length of JO mm. 



a width of 37 mm. 



1 he anterior border has 

 The extent between the lateral angles is jj mm. The hinder border 

 measures \j 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 \~ 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 41 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 less continuous ridges ot quite uniform height, separated 

 by sharp grooves. Usually there are 5 or 6 of these ridges in a line 10 mm. long. On the 

 nuchal scute area these ridges are parallel with the midline. 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 /). reticulata. In the latter the first vertebral 

 scute excludes wholly the costal scutes from the nuchal bone. This bone is far thinner than in 

 /). jloridana. 



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-fig. 

 450). It fits quite accurately against the 

 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 is 

 only 34 mm.; but when we examine the 

 same bone in /). reticulata we find that it too 

 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 downward and strongly backward. 



In the [arman collection is the portion ot 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. The hinder border of the plastron was slightly 

 notcht, as in /). reticulata. At the midline the bone is from 5 mm. to 7 mm. thick. The 

 plastron had a length of about 200 mm. The bone greatly resembles the corresponding part 

 of /). reticulata. 



Fig. 450. Deirochelys jloridana. Nuchal, firs! and 

 second peripherals, and part of first costal. Xi. 

 Partly restored. 



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 wrinkles and grooves; occasionally elaborately sculptured. Hinder border of 

 carapace usually more or less serrated. Plastron with a distinct lip in front and a shallow 



