UERMATHMVDin.i:. 



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 ij mm. Lateralis' it thins to about 9 mm. The hvpoplastron 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- 



einal and behind it a single addi- 

 ct fc> 



tional scute. It seems probable 

 that the latter will be found to 

 have been subdivided, 

 its closest ally, in the following respects: 



perl 



xiph 



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

 from right side. X0.23. Lettering with same 

 signification as in Fig. 315. 



This species appears to differ from A. petrosus, 

 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 



i l 7- 3 l8 - 



.'perl 



per. 2-" 



per.6 



per 11- 



I [GS. ,'17 ami .;iN. -Agomphus tardus. Shell of type. X0.23. 



^i~. Carapace, seen from above, c.p.l, c.p.%, costal plates; n. I, n.%, neural bones; nu. p, nuchal bone; 



per. J, per, u, peripheral bones; py, pygal; spy, suprapygal. 

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



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



bones; xiph, xiphiplastron. 



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. 



