CARBONIFEROUS SPECIES. 81: 



SPIEIFERID^. 

 Genus ATHYRIS, McCoy. 

 Athybis? PERsmuATA, Meek. 



Plate 9, figs. 4,4 a, ib. 



Shell subtrigonal, very gibbous, somewhat longer than wide; lateral 

 margins rounded in outline ; front prominent in the middle ; connecting 

 margins of the valves, on each side of the beaks, broadly and deeply 

 sinuous (see fig. 4 h.) Dorsal valve much more convex than the other, its 

 greatest convexity being at the middle of the front, where it is elevated in the 

 form of a very prominent, rounded, mesial fold, which projects somewhat 

 forward, and scarcely extends back to the middle ; lateral slopes rounding 

 abruptly downward, and considerably produced, so as to meet the margins 

 of the other valve nearly at right angles ; beak strongly incurved. Ventral 

 valve moderately convex in the umbonal region, and depressed in front into 

 a broad, rounded, or somewhat flattened and profound mesial sinus, which 

 causes the anterior margin to project obliquely forward and upward as a 

 linguiform extension filling a corresponding sinus in the margin of the 

 other valve, which it intersects at less than a right angle ; beak unknown. 

 Surface of both valves apparently nearly smooth, excepting rather distinct, 

 subimbricating marks of growth near the anterior and lateral margins. 



Length, about 1.28 inches; breadth, 1.16 inches; convexity, 0.98 inch. 



Although 1 have seen no entire specimens of this shell, those I have 

 had an opportunity to examine seem to differ so widely, not only from all 

 the other forms in the collection, but from any described species of which 

 I have seen figures or specimens, that there appears to be little, if any, 

 reason to doubt that it is a new species. At a first glance, its extremely 

 elevated fold and deep sinus remind one of Bhynchonella acuminata; but, 

 on closer inspection, this fold is seen to be merely rounded, instead of angu- 

 lar, or divided into several smaller ridges, as we see in that shell. I am in 

 some little doubt, however, whether or not it is really a true Athyris, since 

 none of the specimens show the beak of the ventral valve, or, very clearly, 

 any of the internal characters. One internal cast of the dorsal valve shows 

 that it has a mesial ridge, or low septum, in the umbo, much as we often 



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