OF DENISON UNIVERSITY. ^^ 



Crcni])ccten sitb-cardiforinis. "p " 

 (Plate VII, Figs. 4-5) 



Cf. Aviciilopectcn airo/i, Winchei.i., 1863, pars. ? 



[Wrongly quoted above as C. tumidus.] 



We have been caused a great deal of perplexity by this >,,^, .v ^. 

 which occurs by scores in our collection. it is chiefly restricted to a 

 zone about 40 feet below congl. I. though it ranges upward to a hori- 

 zon just beneath it in company with streblopteria media. Aviculopec- 

 ten caroli. Wincliell, would not be considered in this connection were 

 it not for ihe statement made by Prof. Winchell. in 1870, that it was 

 found at Granville, but that the specimens from that locality " were 

 all right valves, and are much flatter than tvpical specimens « f the 

 same vjlve." On the whole it may be safer to regard onr form as a 

 distinct species unless a comparison of lyp-s jiroves this not to be the 

 case. Shell c^f medium or small size, nearly circular, height and 

 length equal, with well-defined and depressed ears. Left valve very 

 ventricose. hinge slightly shorter than extreme length ; lower margin 

 a nearly circular curve intersecting the auricular margin at about two- 

 fifths the distance from the hinge to the lower margin; anterior ear 

 rather large, gready depressed below the adjacent portion of the body, 

 from which it is separated by a sudden deflection ; posterior ear less 

 sharply defined, but nearly ecjually as large and not separated by a 

 well-defined sinus from the body, depressed : beak high, but incurved 

 and acute, projecting slightly beyond the hinge ; greatest convexity 

 near the union of the upper and middle thiuls ; surface marked by 

 from thirty to forty strong, very irregular, radiating coslre, alternate 

 ones being generally smaller and originating by implantation or. more 

 rarely, bifurcation ; these costce are crossed by fiiic, dose, but irregu- 

 lar concentric stria, which do not cross the larger cost;v. and distant 

 undulations; the anterior ear bears about six costic. while the poste- 

 rior ear is nearly smooth, but exhibits more plainly the concentric 

 stride; rarelv two small costic occupy the space between the larger ra- 

 diating ribs.' The right valve is very flat and nearly without markings ; 

 the hinge is longer than or equal to the greatest length and the ears 

 are very large ; and nearly ecpial ; the anterior ear is set oH* by a deep 

 depression from the body and the valve is provided with a deep bys- 



