280 



FOSSIL TURTLES OK NORTH AMERICA. 



is 5 mm. There are eight pairs of costals. Those of the seventh pair join for a short distance 

 behind the seventh neural; those of the eighth pair join their full width. The costals are thin, 

 about I mm. in thickness. There is a single large, roof-shaped suprapygal, whose length is 

 1 8 mm. and whose width is 20 mm. The pygal has a height of 15 mm. and a width of 23 mm. 

 The anterior peripherals are about 12 mm. high, at right angles with the free border. Behind 

 the fifth this dimension increases until in the ninth it is 20 mm. The fourth and fifth are in 

 contact with the hyoplastron; the fifth, sixth and seventh, with the hypoplastron. Fig. 354 

 represents the anterior ends of the, sixth, seventh and eighth. The free border of those in 

 front of the bridge is subacute; that of those behind the bridge, thin and acute. The lower 

 face of the anterior peripherals is smooth, while that of the posterior is sculptured. The 

 latter peripherals have a third, or inner face. This looks toward the interior of the shell and 

 is concave. 



The carapace is exquisitely sculptured, the costals differently from the peripherals. The 

 costals are crost, parallel with the axis of the animal, by low undulating ridges, most distinct 



FIGS. 352 AND 353. Anosteira ornata. Carapace and plastron. X. No. 6132 A. M. N. H. 



352. Carapace. 



353. Plastron, ent, entoplastron; epi, epiplastron; hyo t hyoplastron; hypo, hypoplastron; xiph, xiphiplastron. 



on the distal ends. The nuchal and the peripherals are ornamented by sharper ridges and 

 pustular elevations. In general, the ridges and the rows of pustules on the proximal half of 

 each of these bones run parallel with the costal border. Those on the distal half radiate from 

 a focus placed some distance away from the free border. On the lower faces of the six hinder- 

 most peripherals of each side the radiations extend to the proximal borders. 



The epidermal sulci are narrow and delicately imprest, but most of them may be traced. 

 On the nuchal and the four anterior peripherals the intermarginal sulci can not be seen, 

 owing to the sculpture. On the other peripherals the ascending sulci are easily followed, 

 but the costo-marginal sulci are not visible. From this and other specimens it becomes quite 

 certain that they ran along the upper borders of the peripherals, just below the costo-peripheral 

 sutures. On the pygal a median sulcus ascended about half the height of the bone, then 

 divided and sent a right and left into the costo-marginal sulci. The vertebral scutes appear to 

 have been remarkably modified. The first has a width of 18 mm. in front. We have a right 

 to look for a transverse sulcus crossing this region on the proximal ends of the first costals and 

 the first neural; but there is no trace of it. Instead of this, we find that the sulcus which 



