260 
PALAEONTOLOGY OF NEW YORK. 
Mytilarca regularis, n. sp. 
PLATE XXXII, FIG. 12. 
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 half, 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 strise 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 48 mm. and height 28 mm. 
As compared with M. Chemungensis this species has a proportionally wider 
form; it is more nearly equilateral, the umbonal elevation is less abrupt and 
more nearly central. It is proportionally higher than M. occidentalis and less 
elevated along the umbonal slope. 
Formation and locality. In a sandstone of the Chemung group, near Leon 
Centre, Cattaraugus county, N. Y. 
Mytilarca attenuata. 
PLATE XXXU, FIG. 20. 
Mytilarca attenuata. Hall. Prelim. Notice Lam. Shells, etc., pt. 2, p. 23. 1869. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 32, fig. 20. Jan., 1883. 
Shell above medium size ; body extremely elongate, sub-cuneiform; length 
nearly three times the height; ventral margin nearly straight for almost the 
entire length, with a slight depression at the byssal opening; posterior 
