DERMATEMYDID&. 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 g 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 theentoplastron. The pectoro- 
abdominal crosses in front of the 
hyohypoplastral suture, as in 4. 
petrosus. The abdomino-femoral 
sulcus swings well forward on the 
hypoplastrals. So far as observed, 
there is only an axillary inframar- 
Fic. 316.—Agomphus tardus. Shell of type, seen ginal oie behind it a single: addi- 
from right side. 0.23. Lettering with same tional scute. It Bee e probable 
signification as in Fig. 315. that the latter will be found to 
have been subdivided. 
This species appears to differ from 4. 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 4. tardus is not so thick near the free border, but thicker at the upper 
xiph aes 
Sif 318. 
Fics. 317 AND 318.—Agomphus tardus. Shell of type. 0.23. 
317. Carapace, seen frorn above. c.p.1, ¢.p.8, costal plates; .1, 2.8, neural bones; nu. p, nuchal bone; 
‘ per. 1, per, 11, peripheral bones; py, pygal; spy, suprapygal. ; 
318. Shell, seen from below. ab, abdominal scute; an, anal scute; epi, epiplastron; ent, entoplastron; fem, 
; femoral scute; yo, hyoplastron; hypo, hypoplastron; pec, pectoral scute; per. 2, per.6, per.11, peripheral 
bones; xi ph, xiphiplastron. 
border than in 4. petrosus; the third peripheral is not so long (38mm.) as itis in 4. petrosus (45 
mm.); the upper, or costal, borders of 4. tardus are thicker and the outer end of the hyo- 
plastron has not so strong an upward curve as in 4. petrosus. 
From 4. turgidus this species differs in having the peripherals nearly as thick at their 
costal borders as the maximum thickness. 
