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thin, straight, and projecting, and the mouth widely opeti. 
In //. ventricosa the lip formed by the upper valve is ver}^ 
much curved, so as to come quite over and hide the narrow 
mouth, and in H. digitata the lips are thickened and everted. 
2. Hyalea ventricosa n. sp. (PI. vii., f. 15). 
Almost globular, rounded and much inflated in front ; 
lower valve swollen ; upper valve spoon-shaped, inflated, 
adorned by three keels or ribs radiating from the umbo to 
the extremely reflected and recurved lip ; the central keel 
more pronounced and distinct; the lateral ones broader and 
more rounded; lateral mucrones simply angular, not pointed, 
terminal mucro short and pointed ; mouth narrow, hidden 
by the profusion of the sharp thin lip. Lenth 43^ mill., 
breadth 4 mill. 
Bears some resemblance to H. globulosa Rang and to H. 
quadridentata Les. in general character. In our shell the 
lateral mucrones are single, and there is a decided terminal 
mucro ; the central rib is narrower and more defined than 
the broader rounded one on each side of it. 
3. Hyalea digitata sp. (PI. vii., f. 16). 
Oblong, rather compressed ; lower valve inflated ; upper 
valve slightly convex, adorned with three nearly equal 
rounded radiating ridges, constricted in front, and bordered 
by a thickened lip ; mouth narrow, lips thickened and 
everted ; terminal mucro short, sharji ; lateral mucrones 
.scarcely produced. Length 5 mill., breadth 3 mill. 
In .some respects resembles H. tridentata Bose, and H. 
uncinata Rang, but is not so inflated, and has shorter and 
le.ss curved lateral mucrones. 
