608 TRANS. OF THE ACAD. OF SCIENCE. 
GEN OS "OS TR 
O. QUADRIPLICATA, N. sp. 
Shell small, usually arcuate, rarely elongate-subovate ; 
. j 2 r ; 
longer than wide; anterior and basal margins produced into 
minate at the angles of the border. In nearly all full-grown 
specimens that I have seen, the radiating stri# occupy mere- 
ly the rostral half of the shell. The dimensions of an ave 
rage specimen are— 
Length, 1.30 inches; width, 0.80; thickness, 0.40. 
This is an exceedingly handsome shell, and not liable to be 
staken for any other species. It occurs very abundantly 
associated with Cidaris hemigranosus. 
O, BELLAPLICATA, N. sp. 
Shell of medium size, ovate or subcireular, anal and pallial 
J. 
borders rounded; buccal border subtruncate, valves unequa 
: neave or evel 
d, situated near- 
the anne 
side ; muscular impression large, moderately excavated, ¢ 
gate-ovate, upper edge concave. Surtfac of : 1 aah 0 
with prominent concentric, waved, paeme sie a obtusely 
rate 
growth and form, and from ten to fourteen elev ey 1 radiate 
In many of the specimens before me all of ee 
simple, but in others some of them are bifurcated. remiti¢s. 
individuals they are sharply angulated at igen’ ea more 
The concentric lamine are generally more distinct an 
