«84 PALEONTOLOGY OF NEW-YORK. 



AWcula iiniboirata ( n. s). 



Plate LI. Fio. 6. 



Shell rhomboid, nearly once and a half as long as high : anterior margin 

 broadly rounded ; posterior side narrower and acutely rounded, very 

 convex in the middle and upon the umbo : anterior wing small, acute, 

 extending a little beyond the anterior margin of the shell, and sepa- 

 rated from the body of the shell by a narrow well-marked sinus ; 

 posterior wing larger, separated from the body of the shell by a broad 

 defined sinus. 



Surface marked by concentric lamellose striae, which are closely crowded 

 on the wings. 

 The specimen has nearly all the shell exfoliated, and the small portion remaining 



is somewhat imperfect, the cast retaining the impressions of the lamellose striae. 

 Fig. 6. The left valve, having the posterior wing brolcen off. 

 Geological position and locality. In the pentamcrus limestone of the Lower Hel— 



derberg group : Schoharie county. 



Avicula manticula. 



Plate LI. Fio. 7 & 8. 

 .4rtcuZa manticula : Coxbad, Jour. Acad. Nat. Sciences, 1843, Vol. viii, pa. 241, pi. 12, f. 18. 



Shell " obliquely ovate, acute : anterior wing short and triangular ; 

 " lower valve with unequal, prominent, rather distinct radii ; umbo 

 " narrow, tapering to the summit, which is elevated above the cardinal 

 " line ; basal margin rounded or arched." 



The original specimen from which Mr. Conrad made his description is figured on 

 Plate n. It measures two and a half inches from beak to base, and its greatest width 

 is one inch and a half. The anterior wing is very small, and the posterior wing too 

 imperfect to be determined. The upper part of the shell is very gibbous. The sur- 

 face is marked by narrow radiating ribs, of which about ten are stronger than the 

 others, having one or two smaller ones between. This character is not well repre- 

 sented in the figure. In the specimen, the radiating costse have been originally 

 crossed by concentric striae, some of which w<ere strongly elevated. 



