DERMATEMYDIDiE. 



227 



might expect. The diagrammatic figure has been constructed partly from the type and 

 partly from materials belonging to the Canadian Survey. 



This species was a large one, and it is distinguish by a rather remarkable form of orna- 

 mentation. The length ot the plastron of the type was not far from 670 mm. and the total 

 length of the carapace approximated 775 mm. The form and the elevation probably resembled 

 closely those of the species of Adocus. The sculpture seems to be an exaggerated development 

 of that of the genus just mentioned. It resembles considerably that of some species of the 

 Trionvchidae, but the pits are more commonly arranged in rows, and the intervening ridges 

 are more acute. Often where three ridges meet, there is formed a sharp trihedral elevation. 

 The effect is to produce a very rough surface. There are usually about three rows of pits 



in 10 mm. The whole shell is covered with this sculp- 

 ture. It is best developt on the upper and lower surfaces 

 of the anterior and posterior peripherals. On the upper 

 halves of the peripherals of the bridge it may be obscure. 

 So also sometimes on parts of the plastron, as in the case 

 of the specimen in the collection of the Canadian Survey. 

 The bridge of the plastron is very wide antero-pos- 

 teriorly, the anterior and posterior lobes relatively short. 

 The rims of the lobes are much thickened, the interior 

 portions considerably thinner. The epiplastron of the 

 Canadian specimen (plate 32, fig. 4), which was about 

 as large as Cope's more complete specimen, is 38 mm. 

 thick near its union with its fellow. This thickness 

 diminishes toward the axillary notch, where it is 28 mm. 

 Behind the entoplastron it is only 15 mm. or even less. 

 The epiplastron of Cope's material has an extreme thick- 

 ness of 51 mm. The hyoplastral and hypoplastral bones 

 are only 10 mm. thick where they join. At the inguinal 

 notch the rim of the hinder lobe is 40 mm. thick. This 

 gradually diminishes to 12 mm. near the midline behind. 

 The anterior lobe is about 325 mm. wide and 144 

 mm. long, measured from a line joining the two axillary 

 notches. Its sides slope forward to a rather blunt point. 

 The lateral face of the thickened rim stands at a right 

 angle with the flat lower surface of this lobe. The sculp- 

 ture rises on this face and extends for a distance on the 

 upper surface. 



The entoplastron is large, being about 160 mm. wide, 

 but only 100 mm. long. It is hexagonal, with the lateral 

 borders shortest. 



On the lower surface of the front lobe is found a 

 pair of large intergulars which extend backward to the 

 anterior border of the entoplastron and separate widely 

 the reduced gulars. The humero-pectoral sulcus is at first directed backward from the 

 axillary notch for about 50 mm., then is turned suddenly, forward and inward to the middle 

 of the entoplastron. 



The posterior lobe is approximately 340 mm. wide and only 160 mm. long. It is broadly 

 rounded behind. On the upper surface of this lobe is a large, smooth scar which marks the 

 point of attachment of the pubis. 



The pectoral scutes are narrow at their outer ends. The abdominal scutes are large. 

 The median sulcus pursues a very irregular course from the front to the rear of the plastron. 

 The bridge is remarkably wide, being about 360 mm., considerably more than one-half 

 of the length of the plastron. 



Behind the axillary notch there is a rather short and wide axillary scute, followed by the 

 narrowed lower end of the fourth marginal. The fifth marginal is likewise narrow, but the 

 sixth is greatly expanded. The sc\ enth and eighth are pointed at their lower ends. There is a 



Fig. 287. Basdemys variolosa. Right 

 half of plastron. X '. Mostly from 

 No. 1465 A. M. N. H. 



