226 NOTES ON THE MOLLUSCA OF THE THAMES ESTUARY,
in his opinion that the new Hydrobia was a distinct species, as,
putting aside the difference in the form and contour of the shell, the
tufts and carination of a large majority of the specimens, &c., the
habits and external appearance of the creatures were quite character-
istic. Mr. Marshall frankly acknowledged in his "Further Notes on
British Hydrobiae" (Journal of Conchology, vol. vi., p. 224), that
having always taken Jeffreys for granted, he "had not examined the
animal." I at once sent him living Hydrobiae for comparison. About
this time a correspondent of mine sent me a solitary shell of the true
variety ovata, Jeffreys, of H. ventrosa (which had been authenticated
by Mr. Marshall), affording me the opportunity of comparing it with
specimens of H. jenkinsi, from which it differed considerably.
The examination of the living Hydrobiae and the discovery of the
real variety ovata seemed to convince Mr. Marshall, and soon after-
wards he subscribed to Mr. Smith's opinion that the Plumstead-
Beckton Hydrobia was entitled to rank as a new species. From this,
I conclude that the variety ovata of H. ventrosa is exceedingly rare,
as otherwise comparison of the two shells would have settled the
affair at once. To me it has often been a matter of deep regret that
the splendid collection of Dr. Jeffreys, containing his types, was ever
allowed to go out of this country.
The carination and little tufts upon many of the shells of H.
jenkinsi are very peculiar, and form one of the features by which we
can readily distinguish them from allied species. An examination
with a pocket lens of between two and three thousand shells, from
various places, proves that by far the larger proportion show more or
less traces of the carination, although but few specimens show these
processes in perfection. Amongst the marine and brackish-water
shells of the Antipodes there are quite a number of species of
Hydrobia which are either keeled and tufted, or else possess a number
of delicate hair-like processes, running spirally around the body and
preceding whorls just upon or above the periphery. Several New
Zealand species are strongly keeled, and the shells are either tufted
or sericeous. Potamopyrgos corolla, Gould, is strongly carinated
with a number of very short bristles, proceeding from the keel, and
the very beautiful shells of P. cumingiana, Fischer, have a number
of long silky processes. P. antipodium, Gray, appears generally to
be ecarinate and without tufts or hairs, although a few tufted
specimens may occasionally occur. This species appears most
nearly to resemble H. jenkinsi, and one variety might easily be