LAMELLIBRANCHIATA. 33 



Test thin, marked b^- fine sharp radii, with wider interspaces, which show 

 one, two or three finer rays, crossed by fine crenulating lines of growth. 

 The same characters of marking extend over the ears. 



Internal characters not known. 



The specimen is 14 mm. in length, 12 mm. in height, with hinge-line 

 15 mm. 



This species, in sm-face markings, bears a slight i-esemblance to a young 

 individual of Avkulopedm princeps ; but the undefined ears and proportionally 

 longer hinge-line distinguish it. 



Formation and locality. In the upper layers of the Corniferous limestone ; 

 Young's farm, Williamsville, Erie county, N. Y. 



Section h. 



AviCULOPEOTEN IGNOTUS. 



PLATE I, FKi. 2. 



Avictil(rpectenignotus,Y{ku.. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 1, tijr. 2. J.an., 1883. 



Shell of medium size, transversely and obliquely sub-ovate ; height about five- 

 sixths of the length ; margins regularly rounded, full on the anterior and 

 posterior sides. 



Left valve slightly convex, nearly flat. Right valve unknown. 



Hinge-line straight, central, length nearly equal to the height of the valve. 



Beak obtuse, rounded, low, directed toward the anterior. 



Posterior ear large, broad-triangular, separated from the side of the uml)o 

 by a wide shallow sulcus ; margin slightly concave ; extremity obtuse- 

 angled. Anterior ear less than one-half the width of the posterior, narrow- 

 triangular, separated from the umbo by a deep byssal sinus and a distinct 

 sulcus, extending to the apex of the beak ; margin convex ; extremity 

 rounded. 



Test thin, about .5 mm. in thickness; marked with about twenty-five 

 irregular, rounded radii, which are crossed by very fine concentric strise, and 

 occasionally interrujjted by varices of growth. The rays are conspicuous 



