Figs. 5 and 6.
EOLIS ALDERI, Cocks.
E. griseo-albida, depressa; branchiis subconicis, leviter depressis, seriebus 12—14 crebre digestis,
ordinibus 2 vel B anterioribus albis, reliquis griseo-fuscis, apicibus flavis; tentaculis flavis; angulis
anterioribus pedis paululum productis.
• Eolis Alderi, Cocks, in Naturalist, v. 2, p. 1, pi. 1, f. 1.
Hab. In pools between tide*marks, Gwyllyn Vase, Falmouth, TV. P. Cocks, Esq.
Body five to seven tenths of an inch in length, transparent white, with opaque white
spots. Dorsal tentacles linear, nearly smooth or a little wrinkled, approximating, of moderate
length and bright yellow. Oral tentacles a little longer than the dorsal ones, white tipped
with yellow, set rather above the margin of the head. Branchice very numerous, sub-conical,
a little flattened, and tapering gradually towards the to p ; arranged in from twelve to fourteen
dense rows, nearly covering the whole of the back, extending round the sides of the head in
front, and reaching very nearly to the tail behind. The first two, or sometimes three, rows are
opaque white, the remainder are gray marbled with pale purplish brown, and profusely spotted
with white : the apices are yellow or pale orange with the extreme tips pale. Foot transparent
white, a little rounded in front, and produced into short angles at the sides; the posterior
extremity is extended into a fine point.
For the knowledge of this species we are indebted to our friend Mr. W. P. Cocks, who
found it very abundant at Falmouth in the summer of 1848. During that year, he informs us
that he got nearly seventy specimens. It was scarce in 1849, and from that time to the
present he has not seen a single specimen. It comes very near to our E . glauca, but Mr.
Cocks, who has had the opportunity of studying both species in a living state, considers it quite
distinct. The white ruff, formed by the first two rows of papillae, he assures us is a permanent
and good character in this species, besides that it is never more than half the size of E. glauca
in the adult state, and the colour is also different. Unlike E. glauca, this is a very active and
restless creature, erecting its branchiae and shewing much irritability when disturbed. It
spawned profusely in confinement. The ova, which are deposited in July and August, are contained
in a pellucid membrane of a cylindrical form, attached by the lower surface. From the
drawings we have been favored with, it appears to form a much waved spiral, with a single row
of eggs sparingly distributed through it. In this character the spawn differs from that of any
other British Eolis. Mr. Gosse has observed a similar arrangement of the ova in Antiopa cristata.
The specimen of this Eolis from which our drawing was taken is the only one that reached
us in a living state.
Fig. 5. Eolis Alderi, side view.
6. Two of the branchial papillæ, much enlarged.