260 PALEONTOLOGY OF NEW YORK. 



MyTILABC \ REGTJLARIS, 11. Sp. 



PL \T\: \\\ll. FIG l'->. 



Shell above the medium size: body narrowly ovate ; length less than twice 

 the height; byssal area scarcely depressed ; ventral margin for two-thirds 

 the Length nearly straight, thence curving into the posterior margin which 

 is regularly rounded ; dorsal margin gently curving to the extremity of the 



cardinal line. 



Left valve gently and regularly convex in the posterior hall', convex above 

 and scarcely gibbous on the umbo. Right valve unknown. 



Hinge-line straight, short, oblique. Beak nearly erect, acute and abruptly 

 attenuate. 



Test thin, marked by fine elevated concentric striae which are crowded on 

 the ventral and dorsal sides of the valve. 



Ligamental area narrow, longitudinally striated. 



Interior unknown. 



The specimen described has a length of 4S mm. and height "JS mm. 



A- compared with M. Chemungensis this species has ;i proportionally wider 

 form: it is more nearly equilateral, the umbonal elevation is less abrupt and 



more nearly central. It is proportionally higher than .1/. orcidmtalis and less 

 elevated along the umbonal slope. 



Formation and locality. In a sandstone of the Chemung group, near Leon 

 Centre, Cattaraugus county, N. Y. 



Mttilarca attenuata. 



PLATE XXXII, FIG. 20. 



MytAlt luata, Hall. Prelim. Notice Lam. Shells, etc., pt. •_'. p. :.'::. l- 



Pal. N. Y., vol. v, pt 1. Plates and Explanations : P1.32 



Shell above medium size; body extremely elongate, sub-cuneiform; length 

 nearly three times the height : ventral margin nearly straighl lor almost the 

 entire length, with a slight depression at the byssal opening; posterior 



