CiiAP. III. YOUNG TURTLES. 387 



upper jaw. On tlio top of the head there is a globular elevation, which does 

 not rest merely in the skin ; the height of the hemispheres of the brain them- 

 selves causes the brain-box to rise in this region. The upper jaw shows thus far 

 no sign of the hook, which is so largely developed in the adult ; on the contrary, 

 its lower edge is notched in front. The inner margin of the sheath of this bill runs 

 . fivr backward over the palate, even more so than in the adult, filling up the whole 

 triangle between the alveolar edges. The lower Ijill, however, is provided with a 

 sharp hook, running up^vards. The nostrils lie and open more upwards than in 

 the adult, in which they are directed half forwards. The lower, or rather pos- 

 terior ej-elid, is provided with a comb-like row of scales, which fades entirely 

 away in the adult. The neck is very bulky, and has the same transverse 

 diameter as the head. The shape of the back is oval ; there is a median exca- 

 vation in front for the neck, and two lateral ones for the arms. Behind, the 

 carapace tapers backwards, and runs out into a sharp angle. Three rows of tuber- 

 cles are situated along the back, converging towards the liind end, one of them 

 upon the median, the two others upon the costal plates. (See PI. 6, fig. 15 and 

 IG.) These tubercles begin in the anterior margin of each plate, and rise more 

 and more in a longitudinal direction backwards. Four similar rows of tubercles 

 are seen below, upon the sternal plates, and upon the plates of the bridge. (PI. 

 6, fig. 14.) All these tubercular ridges arise from the thickening of the corium, 

 and are not, as one might suppose, merely owing to a bulging of the epidermal 

 plates. They all vanish also, sooner or later, in the adult, except those in the 

 median line of the back, and two upon the two median rows of i:>lates of the 

 sternum. These ridges of tubercles, the conical shape of the whole trunk, which 

 is far higher than in the adult and tapers backwards nearly to a point, the round- 

 ing and curving of the circuiiiference of the body, instead of exhibiting a sharp 

 and flattened margin as we find it in the adult, give to this young Th. Caouana 

 a general resemblance to Sphargis which is very striking. This is particularlv 

 obvious in a cross-section through the trunk. (See PI. G, fig. 17.) This shows, 

 again, that the Sphargididiu have the lowest standing among the sea Turtles, as this 

 family preserves, in its adult form, features which prevail in the Chelonioidaj only 

 during their earlier development. 



The dorsal plates of the Th. Caouana when hatching show, however, the same 

 great breadth in relation to the length, that we find in the hatching Amyda?; but, 

 while in the latter all the plates increase afterwards in length at the expense of 

 their transverse diameter, in the Chelonioidai the median ones only grow Ion<>-er 

 than broad, while the costal ones grow broader and broader. The marginal plates 

 A-ary in number. We find fourteen in a half grown specimen; while in a series of 

 young ones their number difiers from twelve to fourteen; and again they are of 



