KMYUlD.i:. 



.535 



Echmatemys naomi sp. nov. 

 Plate 51, figs. 1. 2; text-figs. 442-444. 



rhe type ot the present species is a finely preserved shell which was collected by the 

 American Museum expedition of 1903, in the Bridget' beds of Wyoming. The locality is 

 little l)r\ Creek, near the western part of Grizzly Buttes and the level is the lower part of 



horizon B. The shell has suffered slight downward crushing, 

 but none of the characters have thereby been obscured. The 

 number of the specimen is 5975. 



The total length of the carapace (plate 51, fig. 1; text-fig. 

 442) is 360 mm. The width taken across the middle is 263 

 mm., and this is the greatest width. The front of the shell is 

 in no way contracted. The hindermost peripherals appear to 

 have been slightly notcht at the sutures. The table gives the 

 dimensions ot the central row of bones. 



The width of the free border of the nuchal is 42 mm. The 

 costals present little that is novel. The proximal ends are 

 usuallv ot nearly the same width as their distal ends, except that 

 the last three have their distal ends expanded somewhat. 



The table below presents the dimensions of some of the 

 peripherals. The height of the third peripheral is 53 per cent, of the hinder border of the 

 first costal. 



The nuchal and the first pair of peripherals have an acute free border. The greatest thick- 

 ness of the first is 19 mm. The free border of the second is subacute and passes into the 

 rounded free border of the third. 



The posterior peripherals are flared moderately upward. They are rather thin and pass 

 out into a sharp, thin, free border. The thickness of the ninth at the longitudinal sulcus is 

 9 mm. 



The first costal is four-fifths as wide, fore and aft, as it is lung on the hinder border. 



The upper surface of the shell is very uneven. Large parts of the sulci run in very deep 

 grooves. Between them the surface is usually rough and pitted. There is no keel. In the 

 middle of the nuchal there is a slight, broad, rounded, longitudinal elevation and a similar one 

 on the suprapygals and pygal. The sulcus running around the carapace on the nuchal, the 

 peripherals, and the second suprapygal, lies in a deep groove. This groove has so weakened 

 the peripherals in its course that the pressure has caused them to yield along this sulcus. The 

 sulci between costals I and 2 and between 2 and 3 lie in very deep grooves, especially at their 

 upper ends. The hinder ends of the sulci bounding laterally the tbree anterior vertebral scutes 

 lie in deep and broad grooves. The sulci between many of the marginal scutes occupy 

 deep grooves. 



The nuchal has a length of a; mm. and a width of 15 mm. 



The dimensions of marginal scutes are shown in the table above. 



The costo-marginal sulci run far below the costo-peripheral sutures. 



The vertebral scutes are broad and rather strongly urn-shaped; their dimensions are pre- 

 sented in the table above. 



The plastron (plate 51, fig. 2; text-fig. 443) has a total length of 326 mm. The front 

 extends somewhat bevond the border of the carapace. The length of the anterior lobe is 06 



