CLASS GASTROPODA 
243 
not thickened, very regularly and finely crenulated at all stages of growth; 
internal callus-rim of perforation somewhat excavated posteriorly in young 
shells. (Tryon and Pilsbry, Manual of Conchology.) 
Type. Lucapina crenulata Sowerby. 
Distribution. Monterey Bay, California, to Lower California. 
Megathura crenulata Sowerby, 1825 
Tankcrville, Catalogue, Appendix 6. Conchological Illustrations, Fissurella, fig. 18. 
F. testa oblongo-ovata, depressa, alba; foramine ovato, integro; super- 
ficie striis confertis, radiantibus, decussatis; margine crenulata. Long., 
3% 0 ; 2 X / 10 unc. (Sowerby.) 
Shell oblong-ovate, somewhat irregular, deeply convex, radiately finely 
and very closely ridged, ridges transversely very finely striated with obso¬ 
lete scales, orifice large, nearly orbicular, basal margin crenulated; pinkish 
fulvous-color. ( Conchologia Iconica .) 
Type in Tankerville Collection. Type locality, Monterey, California. 
Range. Monterey Bay, California, to Cerros Island, Lower California. 
Genus MEGATEBENNUS Pilsbry, 1890 
The small species grouped under this name agree with Fissurellidae 
(as restricted to Orbigny’s type) in having a partially internal, large- 
apertured shell, a mantle ample enough to cover the entire dorsal surface 
of the foot and head, its edges entire; they differ from Fissurellidae in 
the much greater proportional size of the shell, more elevated body, the 
foot (viewed ventrally) almost as extensive as the mantle, the margin of 
the latter not at all thickened, and the shell not white-bordered above. 
(Pilsbry.) 
Type. Megatebennus bimaculata Dali. 
Distribution. Cape of Good Hope, West Africa, Benguela, South 
Africa, Natal, Australia, Tasmania, New South Wales, California. 
Megatebennus bimaculatus Dali, 1871 
Plate 85, fig. 15 
American Journal of Conchology, 7:132; PI. 15, fig. 7. 
Shell ellipsoidal when young, subquadrangulate, and a little narrower 
in front than behind, when adult. Aperture the same shape as the shell, 
slightly encroached upon in some specimens by a point on each side. 
External surface furnished with radiating, round costae, not bifurcating 
but widening slightly toward the margin. These are crossed by evident 
but not very strong lines of growth, which in some individuals are rather 
[845 ] 
