322 AMERICAN TESTUDINATA. Part II. 



is here little more than a hroad girdle encircling the thorax and abdomen. The 

 carapace has no sharp distinct marginal rim, but curves round over the outer 

 edge and meets the plastron somewhat under the body; this curved outer edge 

 rises constantly backwards. 



The carapace is strengthened by several longitudinal ridges, the most prominent 

 of wliich is along; the middle of the back: it is low and small at the front end, 

 but f-rows hi"-her and broader backward, until just over the sacrum it includes 

 the whole width of the carapace, thence it lowers to the hind end, making this 

 narrow, unsupported part of the shield nnich firmer than it would be if it was 

 flat on each side. Beginning at the angle of the truncated front end is another 

 rido-e, hio'hest at the front end and diminishing backward, so that near the front 

 end the two together render the top of the l)ody nearly flat; but over the pelvis 

 they change the curve of the surface but little. There are two more pairs of 

 ridges outside, but they are quite small, and the lowest one little more than a 

 row of bony nodules. The dermal shield, as in all Turtles, rests upon the verteljral 

 column of the thoracic and abdominal regions, upon tlie ribs, upon the isolated 

 true bone above the lower neck vertebrjB, and iipoii the true bones of the ster- 

 num. (.>ver all these is wrapped a thick layer of coarse fibrous corium.^ In the 

 carapace, this filjrous corium is protected and stiffened by an overlying sheet of 

 bony pavement. This pavement' nowhere rests upon or touches the true skele- 

 ton ; it is perfectly continuous, without any other suture than those of its pave- 

 ment-like structure, and without hitervals above the ends of the ribs. This bony 

 sheet curves with the carapace at its lower edge, but does not extend over the 

 plastron. The ridges of the carapace, spoken of above, are made by angles in 

 this sheet, fdled up Ijelow by an increased thickness of the corium, but the lower 

 surface of the latter has no corresponding depressions. Along each of the ridges 

 is a vo\Y of nodules. In the plastron, the thick layer of fibrous corium is not at 

 all protected by a bony sheet, and has no bony derm, excepting some rows of 

 nodules ; these rows are somewhat irregidar, but there are, in general, five of 

 them, a double one along the middle, and two single ones o)i each side. The 

 corium is supported on its inner surface by the true bones of the sternum, of 

 which there are four pairs ; these are long, narrow, and arranged in a contin- 

 uous row, encircling the flattened, horizontal surface. The foremost pair meet 

 between the fore legs, and at their meeting are broad and strong; they spread 

 apart backward, and overlap the outside of the second pair ; the latter send out 

 a process behind each shoulder ; the second and third pairs extend the whole 

 length of that part of the plastron which spreads entirely across the body, and 



» See Chap. 1, Sect. 4 and 5, ji. 2.5C and 263. ^ See Chap. 1, Sect. 5, p. 26 i. 



