114 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.56. 



genus Neurankylus yet discovered. The other two species, N. 

 eximus Lambe, being from the Belly River formation of Canada, 

 and N. haueri Gilmore, from the Kirtland formation of New Mexico. 



All of the carapace in front of the posterior half of the second 

 vertebral scute is missing; likewise, all of the plastron slightly in 

 advance of the inguinal notches. The shell has been pressed fiat 

 dorsoventrally, but the outlines of the part preserved appear to be 

 but little distorted, and undoubtedly give a correct conception of 

 the form of the shell. None of the sutures between the bones can 

 now be observed, all traces being obliterated by their complete coa- 

 lescence, due, no doubt, to the old age of the individual. The sulci 

 defining the dermal scutes, however, can in most instances be clearly 

 made out, as shown in Plate 29. 



The presence of an ornamentation over all the external surfaces 

 of the shell at once distinguishes this form from the two species 

 mentioned above. This sculptm-e is composed of low, fiat-topped 

 ridges and elevations, the ridges usually being wider than the 

 intervening valleys, which are often threadlike. They form rather 

 a imiform roughening of the smiace but do not have any definite 

 pattern. 



There is no indication of an interrupted median carina such as is 

 present in the neiu-al region of N. haueri. 



The presence of this ornamentation over the external surfaces of 

 the shell, the relatively narrower vertebrals, and relatively wider 

 posterior plastral lobe with a truncated posterior end, constitute a 

 combination of characters indicating the distinctness of this specimen 

 from the other described forms and the name Neurankylus wyoming- 

 ensis is proposed for its reception. 



In form the part of the carapace preserved resembles that of N'. 

 haueri being broadly but evenly rounded, not scalloped, as in the 

 former species, except that they agree m having a wide posterior 

 median notch. It is estimated that the length of the entii'e shell 

 was about 530 millimeters; the greatest width is 475 millimeters. 

 The border anterior to the inguinal notches is thickened and rounded, 

 but posteriorly it becomes thinner, though the edges are obtusely 

 roimded, not having the thin acute border of iV. hauen. There was 

 probably a slight flaring upward of the peripheral bones, though 

 they have been quite flattened by the pressure to which they were 

 subjected. 



The sulci are narrow and faintly impressed. The vertebral scutes 

 are relatively narrower than in either N. eximus Lambe or N. haueri 

 Gilmore. The principal dimensions of these scutes are given in the 

 table. 



