242 



FOSSIL TURTLES OF NORTH AMERICA. 



the hyoplastron in front of the axillary notch is acute, differing thus from A. agilis and A. 

 beatus. The hyoplastral and the hypoplastral portions of the median suture are nearly equal 

 in extent; whereas in A. agilis the hypoplastral portion is considerably longer than the hyo- 

 plastral part. The transverse suture between the anterior and posterior halves of the plastron 

 is very coarse, there being alternately large pits and processes for mutual gomphosial articu- 

 lation. The form and proportions of the hinder lobe may be determined from the table on 

 this page and from the figure. The free borders are acute, with a parallel groove on the upper 

 surface. The scar for the pubis resembles that of the other species, but it is more deeply 

 imprest. Just in front of the hinder border of the xiphiplastrals and lying across the midline 

 there is a conspicuous elevation, the thickness of the bone here being 16 mm. In the center 

 of the lobe the bone thins down to about 10 mm. 



The pectoral scutes are of considerably greater extent antero-posteriorly than in A. agilis, 

 68 mm. as opposed to 36 mm., the humero-pectoral sulcus swinging well forward on the ento- 

 plastron. The abdominal scutes are larger than those of any of the five species compared 

 with this one in the table, the sulcus between them being 135 mm. long. The femoral scutes 

 also exceed those of the other related species, being 100 mm. in the midline. The anal scutes 

 are relatively short, 75 mm. There are 3 inframarginal scutes on the bridge, the middle one 



Table of measurements of species of Adocus. 



being 107 mm. long and 28 mm. wide. In the figure the sulci are represented as being broader 

 than they really are. 



The plastron is considerably eroded. The lower surface is furnisht with numerous small 

 pits, some of them resembling pin-holes, but to what extent these are due to weathering it is 

 difficult to say. 



The anterior rim of the carapace, from one axillary notch to the other, shows that at 

 these notches the carapace had a width of 455 mm. Whether or not the carapace expanded 

 backward, as it does in A. punctatus, can not now be decided. The front (plate 34, fig. 8) 

 is almost exactly an arc of a circle whose radius is 197 mm. The front of 'A. punctatus is 

 somewhat truncated. The rim is thick and heavy, except that the nuchal bone is excavated 

 on its hinder surface, so that its thickness is only 14 mm. At its articulation with the first 

 peripherals it has increased to 25 mm. The greatest thickness of the third peripheral, just 

 in front of the axillary notch, is 40 mm. 



The upper surface of the nuchal and of the anterior peripherals is slightly convex from 

 above downward. The free edge is rather thin and is somewhat reverted, as in A. punctatus. 

 The lower side of the peripherals is very convex from front to back; that of the nuchal con- 

 cave. The free border of the nuchal measures 75 mm. At its upper, or hinder, border it 



