110 



FOSSIL TURTLES OF NORTH AMERICA. 



The fore-and-aft width of the first costal is 64 mm. at the proximal end; its greatest width 

 was about 90 mm. Its length is estimated at 120 mm. On the lower side, at the distal end, is a 

 deep triangular excavation, 40 mm. long, for the axillary buttress. From it a broad ridge 

 ascends to the rib-head of the costal. In front of the ridge, along its proximal third or more, 

 is another ridge, sharper and more prominent, representing the first rib. 



The fifth costal is 6 mm. thick at its distal end. On the under surface of the distal end is an 



excavation for the inguinal buttress, a groove ascending about 60 mm. above the peripheral 



border and 6 mm. wide. It is deepest at the upper end, becoming very shallow at the lower end. 



The seventh and the eighth costals are modified for close articulation with the ilium. On 



the seventh the thickening produced by the rib proper lies near the hinder border of the bone. 



The hinder part of the thickening is excavated somewhat, espe- 

 cially near the proximal end of the costal, to form a broad groove 

 for the ilium. The proximal end of the groove is closed partly 

 by the ridge proceeding from the rib-head of the eighth costal and 

 partly by a subcubic bone, which appears to be the tenth rib. 

 This lies in a depression of the eighth costal. The iliac groove 

 is 18 mm. wide at its upper end; and here its bounding walls are 

 most prominent. Behind the ridge limiting the groove posteri- 

 orly is another groove, shallower and roughly excavated, which 

 appears to have lodged a bone, probably the first sacral rib. 



The surface of the carapace is even, but it is sculptured everywhere by a network of 

 shallow grooves. On the costals the network is the coarsest, the grooves lying from 2 mm. to 



5 mm. apart and mostly directed parallel 

 with the length of the costal. On the 

 neurals and peripherals the network is 

 much closer. 



The sulci of the carapace are broad 

 and shallow. There is no nuchal scute, 

 the first marginals joining at the midline a 

 distance of 44 mm. The length of the sul- 

 cus between the first and the second margi- 

 nals is 44 mm.; that between the second 

 and the third, 23 mm. The sulcus between 

 the eighth and ninth marginals, on the 

 eighth peripheral, is 37 mm. long; the next 

 one, 31 mm.; the next, 27 mm. 



The vertebral scutes of this species are 

 much narrower than those of T. leslianus, 

 as shown by the table above. 



The sulcus between the fifth vertebral 

 and the hindermost marginals falls behind 

 the suprapygal. 



The exact length of the plastron (fig. 

 102) can not be determined, the connection 

 between the epiplastron and the hyoplas- 

 trals not being present. The length was, 



tic. 102. Taphrosphys longtnuchus. Plastron of 

 type. Xj. Known portions represented by 

 stippled areas. 



however, not far from 340 mm. The notch 

 in the rear of the plastron was about 30 

 mm. deep, so that the length along the 

 midline was about 310 mm. The epiplastrals are relatively small, especially when compared 

 with those of Hydromedusa. The hinder end of each is broken off, but each was probably 

 about 70 mm. long. The width was about 33 mm., while the greatest thickness of the outer 

 end is 7 mm. The free border is acute at the midline, becoming subacute distally. Cope 

 describes, under the name of mesosternal, a portion of the entoplastron, but this is now lost. 

 He did not give the dimensions. He states that the extremities are acute-angled and that 

 the bone was even more transverse than it is in T. molops. 



