TESTriMNin.'V. 



375 



In large fragment of sandstone that had fallen from the bluff. Nov. 19, 1876. D. Baldwin." 

 Another label states that the specimen came from the "Eocene Bad Lands. Gallina, New 

 Mexico." This locality appears to he in Rio Arriba County, of the territory mentioned. 

 The deposits whence the shell was derived are in all probability a portion of the \\ asatch. On 

 the carapace is found Professor Marsh's receipt number 927. 



The specimen is somewhat distorted and injured by pressure, being slightly comprest and 

 thrust toward the left side. Crushing has also affected the upper median region, so that most 

 of the neurals have been displaced. At a later time these were weathered and fractured; and it 

 is now quite impossible to restore them to their proper positions. The right border from the 

 fifth peripheral to the tenth has been weathered and removed. In the same way the right side 

 of the hinder part of the plastron has been damaged. 



The length of the carapace (plate 59, fig. 1 ) in a direct line is 550 mm. The greatest width 

 was at least 440 mm. In form it was high and archt. Over the limbs the peripherals were con- 

 siderably flared. The anterior border was truncate; the hinder border rounded and scallopt. 

 The free borders of all the anterior and posterior peripherals have acute edges. 



On account of crushing the dimensions of the nuchal bone can not be determined. Appar- 

 ently it extends backward but little further than the first peripheral. While portions of most of 

 the neurals remain, little regarding them can be said. The seventh has a length of 40 

 mm. The eighth is small. There are apparently 3 suprapygals. ( )f these the anterior 

 appears to have been 23 mm. long and to have had an anterior concave and a posterior convex 



border. The second suprapygal is bifurcate, with the lateral 

 branches resting on the eleventh peripheral. The third supra- 

 pygal is lozenge-shaped and is included between the branches 

 of the second suprapygal bone and the pygal. The costals 

 vary considerably in width; but unlike those of the species of 

 Testado, the upper and the lower ends differ little in width. 

 The table herewith gives the dimensions of the costals, excluding 

 the first. 



The peripherals are large, those of the bridge region rising 

 much higher than in H . corsoni. The first and second each 

 occupy about 80 mm. of the free border of the carapace and 

 extend backward from the border 72 mm. Those of the bridge region rise a distance of 

 90 mm. above the slight carina which runs from the free edge of the third peripheral to the 

 edge of the seventh. The eleventh peripheral rises 70 mm. from the free border. The 

 pygal is 45 mm. high in the midline; 62 mm. wide at the upper border; and 40 mm. wide 

 at the lower border. The upper border is notcht for the lower border of the hindermost 

 suprapygal. 



The sutures between the bridge peripherals coincide at their upper ends closely with those 

 between the costals, except that between the fourth and fifth peripherals. The sutures between 

 the bridge peripherals and the plastral bones appear to have been obliterated. 



The sulci between the dermal scutes of the carapace are narrow and shallow, but most of 

 them lie in rather deep grooves in the bones. Of the vertebrals none can be satisfactorily mapt, 

 except the fifth. This is about 150 mm. wide behind. Its anterior border appears to have 

 crost the eighth neural. It is probable that the others were narrow. The sulci between the 

 costal scutes and the marginals follow closely the sutures between the costal and the peripheral 

 bones, except that in front the sulci lie on the nuchal and the first and second peripheral 

 bones; while in the rear the sulcus crosses from side to side the hindermost suprapygal. There 

 are two very distinct supracaudal scutes, a right and a left. 



The total length of the plastron ( fig. 472) was about that of the carapace, 530 mm. The 

 anterior lobe extends somewhat in front of the anterior border of the carapace, and has a length 

 of 180 mm. The width was at least 266 mm. There is a rather prominent lip, which projects 

 beyond the general border of the lobe. This lip is truncated, or only slightly rounded in front. 

 The width at the base is 120 mm., in front' about 88 mm. The free borders of the lobe are 

 subacute, but the front of the lip is considerably thickened. On the upper side the thicken- 

 ing increases until if is 33 111111. There is on this upper surface a median ridge, on each side 

 of which is a longitudinal valley. 



