d was apparently
gregarious. Mr. Macgillivray states that it is furnished with a float in
the manner of Ianthina. The largest specimens measure rather less than
two lines in diameter. The shell is of a yellow horn colour (as is also
the operculum) thin and transparent. It bears a striking resemblance to
our much more minute Jeffreysia opalina. The four tentacula and the form
of the very peculiar operculum also seem to indicate considerable
affinity with the genus Jeffreysia of Alder, and an examination of the
remains of the tongue extracted from a dried specimen showed an
arrangement and form of the lingual denticles very closely resembling
that exhibited by Jeffreysia. On the other hand, the very distinct and
long siphonal tube delineated in Mr. Macgillivray's drawing, taken when
the animal was alive, would seem to refer this genus to some family
probably near to Cancellaridae. It is certainly entirely distinct in
every respect from any known Gasteropod. It is a form of very great
interest to the geologist, for in it we see the nearest representation of
certain palaeozoic (especially Lower Silurian) univalves hitherto
referred to Littorina, but which, judging from their associates and the
indications afforded by the strata in which they are found, were
assuredly either inhabitants of deep water or floaters in a great ocean
like the Pacific.

I have dedicated this most interesting creature to my friend Mr.
Macgillivray, its discoverer, whose researches have been productive of so
much new and valuable contributions to all departments of zoological
science.

I have named the species M. pelagica. Tab. 3 fig. 8. a, b, c, d. (Mus.
Brit. and Geol.)

New Genus--CHELETROPIS, Forbes.

Shell spiral, turbinate, dextral, imperforate, spirally ridged or
double-keeled and transversely wrinkled; spire prominent, its nucleus
sinistral; aperture ovate, canaliculated below, its outer margin
furnished with two claw-like lobes, the one central and formed by a
prolongation of the margin between the keels of the body whorl, the other
smaUer and nearer the canal; peristome thickened, reflexed, forming a
conspicuous margin.

Operculum none ?

Animal unknown, but certainly floating, and probably pteropodous. This I
infer from its habits, and from the analogy of the shell with Spirialis.
(Mus. Brit. & Geol.)

The only known species, C. huxleyi (dedicated to Mr. Huxley, Assistant
Surgeon of the Rattlesnake, and now eminent for the admir