3^3 



It is unfortunate that so many of the specimens which must be referred to this species are 

 devoid of exact records regarding their levels and localities. 



Echmatemys arethusa sp. nov. 



Plate 49, figs. I, 2; text-figs. 421, 422. 



The present species is founded on a single specimen which was collected by the American 

 Museum expedition of 1903 into the Badlands in the vicinity of Bridger, Wyoming. The 

 locality in which it was obtained is the western portion of Grizzly Buttes and the level the 

 lower portion of horizon B. The catalog number of the specimen is 5920. 



The specimen lacks most of the left peripherals, all of those behind the ninth, and most of 

 the xiphiplastrals. It has likewise been crusht toward the left side. 



The length of the plastron to the front of the xiphiplastrals is 225 mm., from which we 

 estimate that the whole length of the plastron has been close to 292 mm. and the length of the 

 carapace, 328 mm. 



With the exception of faint longitudinal stnations, the surface of the carapace (plate 49, 

 fig. i) is smooth. The fourth vertebral scute is traversed by a low rounded keel. 



The nuchal and first neural have been fractured so that 

 their exact dimensions can not be determined; but the free border 

 of the nuchal was close to 48 mm. and the length was close to 50 

 mm. The neurals furnish the measurements shown in the table. 

 The free border of the nuchal and first pair of peripherals is 

 acute. The sulci of the carapace are narrow and not deeply 

 imprest. The vertebral scutes are narrow and the sides of the 

 second, third, and fourth are nearly parallel. The table below 

 presents the dimensions of some of the peripherals, and of some 

 of the vertebral and marginal scutes, so far as determinable. 

 It will be noted that the fifth vertebral is unusually wide. 

 The nuchal scute has a width posteriorly of 9 mm. Its length can not be determined. 

 The costo-marginal sulci run a moderate distance below the costo-peripheral sutures. 



As already stated, much of the plastron (plate 49, fig. 2; text-fig. 421) is missing. The 

 length of the anterior lobe is 78 mm.; the width of its base is 144 mm. The length is therefore 



Dimensions of marginal scutes. 



XT Height Greatest ,/ m 



N - in front, height. , f f . ree 

 border. 



27 



39 



28 



35 

 42 



35 



39 



43 



40 



4 o 



only 54 per cent, of the width. From the axillary notches its free borders curve regularly to the 

 epiplastral lip. This is narrow, 40 mm.; large lateral tooth just within each gular sulcus. 

 There is a projecting tooth in the midline and on each side of it a minute tooth. On the upper 

 side of the epiplastrals (fig. 422) the gular scutes expand until they have a width of 65 mm. 

 The thickening of the epiplastrals on the upper side extends backward from the tip of the 

 median tooth 23 mm. The greatest thickness of the epiplastrals is 13 mm. Just outside of 

 the gular sulci, on the upper side, the horn-covered surface is 12 mm. wide; at the suture with 

 the hyoplastrals, 14 mm. The entoplastron has a length of 50 mm. and a width of 58 mm. 

 The thickness of the plastron at the crossing of the median suture and that between the hyo- 

 plastrals and hypoplastrals is 15 mm. 



The width of the bridge is 116 mm. 



The length of the hinder lobe can not be determined. Its width at the base has been 146 

 mm. The inguinal buttresses arise about half-way from the border of the hinder lobe to the 

 midline, 



