DERMATEMYDIDJE. 



253 



The entoplastron is not present, but the notch in the front of the hyoplastron shows that 

 the entoplastron was broadest behind. Its width was about 45 mm. The hyoplastron (fig. 

 318) is 60 mm. long on the midline and about 100 mm. wide. Its greatest thickness, at the 

 midline, is 27 mm. Laterally it thins to about 9 mm. The hypoplastron is 62 mm. long on 



the midline, 95 mm. wide, and 31 

 mm. thick. The bridge was about 

 106 mm. wide. 



No sulcus has been observed 

 crossing the front of the hyoplastron 

 and the entoplastron. The pectoro- 

 abdominal crosses in front of the 

 hyohypoplastral suture, as in A. 

 petrosus. The abdomino-femoral 

 sulcus swings well forward on the 

 hypoplastrals. So far as observed, 

 there is only an axillary inframar- 

 ginal and behind it a single addi- 

 tional scute. It seems probable 



perl 



xiph 



FIG. 316. Agomphus tardus. Shell of type, seen 

 from right side. Xo.23- Lettering with same 

 signification as in Fig. 315. 



that the latter will be found to 

 have been subdivided. 



This species appears to differ from A. petrosus, its closest ally, in the following respects: 

 The marginal scutes extend higher on the peripheral bones; the second peripheral is relatively 

 higher; this peripheral of A. tardus is not so thick near the free border, but thicker at the upper 



3 l8 - 



ffiper. 6 



per.lt- 



FIGS. 317 AND 318. Agomphus tardus. Shell of type. Xo.23- 



317. Carapace, seen from above. c.p.i, c./i.8, costal plates; n. I, .8, neural bones; nu. p, nuchal bone; 



per. i, per, II, peripheral bones; py, pygal; spy, suprapygal. 



318. Shell, seen from below, ab, abdominal scute; an, anal scute; epi, epiplastron; ent, entoplastron; fern, 



femoral scute; hyo, hyoplastron; hypo, hypoplastron; pec, pectoral scute; per. 2, per. 6, per. 1 1, peripheral 

 bones; xiph, liphiplastron. 



border than in A . petrosus; the third peripheral is not so long (38 mm.) as it is in A. petrosus (45 

 mm.); the upper, or costal, borders of A. tardus are thicker and the outer end of the hyo- 

 plastron has not so strong an upward curve as in A . petrosus. 



From A. turgidus this species differs in having the peripherals nearly as thick at their 

 costal borders as the maximum thickness. 



