LAME/JJIl/UNCIirATA. 33 



Test thin, marked by fine sharp radii, with wider interspaces, which show 

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

 The saint' characters of marking extend over the ears. 



Internal characters not known. 



The specimen is 11 nun. in length, \- nun. in height, with hinge-line 

 15 mm. 



This species, in surface markings, hears a slight resemblance to a young 

 individual of Aviculopecten princeps ; hut 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 b. 



Aviculopecten kjnotus. 



PLATE I, FIG. -'. 



AvietUopeeten ignotus. Ham.. Pal. N. Y.. vol. y, pt. I. Plates and Explanations: PI. I. fig. 2. .Ian.. 1883. 



Shell of medium size, transversely and obliquely sub-ovate; height aboui live- 

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

 posterior sides. 



Left valve slightly convex, nearly tlat. 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 umbo 

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

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

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

 sulcus, extending (<» the apex of the beak; margin convex; extremity 

 rounded. 



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

 irregular, rounded radii, which ore crossed by very tine concentric Btriae, and 

 occasionally interrupted by varices of growth. The rays are conspicuous 



5 



