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274 American Seashells
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.
EYE
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Mfti-e
OP£NINCi
BEHIND UOb€ 'MftNTLC
MftNTue
CftVVTV OPENING
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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