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274 strong, axial ribs, but the last 2 whorls with only numerous fine spiral threads crossed by exceedingly fine growth lines. Aperture elongate, rather ex- panded and a little flaring below. Sinus moderately large and simple. Color cream with yellowish brown maculations. Uncommon from shallow water to 25 fathoms. Subclass OPISTHOBRANCHIA (Bubble-shells, Pteropods, Sea Slugs) Order ONCHIDIATA Family ONCHIDIIDAE Genus Onchidella Gray 1850 Without a shell, animal slug-like, low, oval, with two short tentacles or eyestalks at the end of which are the eyes. Mantle entirely covering the back; respiratory, anal and female genital pores at the posterior underside; male pore below the right tentacle and above the sensory lobe. Shallow water to intertidal. Formerly placed in the pulmonates, but now beheved to be an early offshoot of the opisthobranchs. See Freter, 1943.

Figure 58. Underside of the marine slug, Ojichidella, % inch.

Onchidella floridana Dall Florida Onchidella West coast of Florida, the Lower Keys and Bermuda. V2 inch in length, uniform slaty-blue to dark-gray; underside bluish white, with a greenish tinge to the veil. Dorsal surface velvety. Mantle margin with about 1 00 whitish, elongate tubercles. Common along the shore at low tide. Lives in rock crevices in nests, returning home after browsing at low tide. Onchidella carpenteri Binney Puget Sound to Lower California. Carpenter's Onchidella