CORONULA BISSEXLOBATA. _De Blainville._ Dict. des Sciences
Naturelles, tom. 32, (1824), Tab. 117, fig. 1.
PLATYLEPAS PULCHRA. _J. E. Gray_ (!). Annals of Philosophy, (new
series), vol. 10, (1825).
COLUMELLINA BISSEXLOBATA. _Bivona_ (fide _Philippi_). Nuovi generi di
Mollusch. (1832), Tab. 3, fig. 1.[126]
CORONULA CALIFORNIENSIS. _Chenu_ (!). Illust. Conch., Tab. 1, fig. 4.
[126] This memoir was published in the 'Effemeridi Scientifiche e
Litt. per la Sicilia,' according to the 'Bibliographia Zoologiæ et
Geologiæ,' by Agassiz and Strickland.
_Shell with the transverse lines of growth conspicuous: parietes
permeated by pores; sheath descending barely half-way down the
parietes._
_Hab._--Mediterranean, attached to turtles. River Gambia, attached
to manatee. Honduras, attached to manatee. Moreton Bay, lat. 27°
S., Australia, apparently attached to the dugong of that coast.
California(?) Mus. Brit., Stutchbury, and Cuming.
_General Appearance._--Shell generally much depressed, and broadly
oval or circular; sometimes steeply conical. Orifice oval, generally
not large. Surface rather plainly marked by closely approximate
lines of growth, which with the lobed outline gives to the whole an
elegantly sculptured appearance: occasionally the longitudinal ridges
formed by the parietal septa are distinct. Basal diameter of largest
specimen three quarters of an inch.
_Structure of Shell._--I have nothing material to add to the generic
description. The midribs are not so prominent as in the following
species, and hence the basal membrane is less convex. The origin
of the midrib as a fold is very plain. The sheath descends barely
half-way down the walls, and is a little hollow on its under margin,
on each side of the midrib. Beneath the sheath the parietes are
finely ribbed (fig. 1 _d_), but to a variable degree. I may here
remark, that in the specimens taken from manatee, on the coast of
Africa and at Honduras, the internal ribs extended further up and
were plainer, and the opercular valves seemed to be a little narrower
than in the other specimens, so that I at first suspected that they
were specifically distinct, but I could make out no other than these
small and variable points of difference.
_Scuta_: oblong (fig. 1 _c_), about twice as long as broad, with the
rostral end rounded, rather narrower than the other end, and curled a
little inwards. _Terga_, of nearly the same shape and nearly as long
as the scuta: the carinal end is rather more pointed than the scutal
end of the valve, and when viewed internally, the growing surface
of this end is seen to be bluntly pointed. In both valves the upper
layers of shell usually scale off.
_Mouth and Cirri._ The only differences, compared with the following
species, that I perceived, were that the hairs at the end of the
palpi were here rather longer, and the fourth tooth in the mandibles
rather less distinct. The rami of the first cirrus are very unequal
in length.