. Carnegie Institution of Washington publication. 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 me
. Carnegie Institution of Washington publication. 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 gradu
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