Mr. W. Clark on the Littorinide. 357 
without any particular concurrence therein, recorded these opi- 
nions in their interesting work. But in corroboration of these 
views I shall adduce some considerations on another genus, 
which has largely contributed to the increase of pseudo-species ; 
I allude to that portion of the genus Littorina designated L. lit- 
torea and L. rudis. 
I now take a rapid glance at the family of the Littorinide, and 
then conclude my paper by giving the notes and specific descrip- 
tions of the types of each genus as proofs, and in support of what 
I have advanced, and to afford data to malacologists to come to 
just conclusions on what I have submitted to their consideration. 
LitToRINID&. 
This well-known family as now constituted consists of the 
genera Lacuna, Assiminia, Rissoa, and Littorina. he Lacune of 
authors are scarcely distinguishable from the Littorina littoralis ;. 
the animals are all but identical, and the two genera appear to be 
separated on conchological grounds,—the groove in the columella 
rather than an animal distinction. I think it would conduce to 
the interests of science if the Lacune were merged in the genus 
_Litiorina, and marched pari passu with Littorina littoralis as 
species. 
I shall show malacologically, in a memoir I am preparing on 
the Lacuna, that the difference of the animal of Lacuna and Lit- 
torina littoralis is scarcely appreciable. The Lacune have only 
one or two species instead of the eight or ten of authors. 
Assiminia was established by Mr. Gray, and differs chiefly from 
the Rissoa ulve and R. subumbilicata of Montagu, in having the 
eyes fixed at the extremities of the tentacula, m consequence of 
being placed on adnate pedicles of concurrent length. 
The Rissoe are very minute ; they inhabit the littoral and la- 
minarian zones; the types of the first zone are the Kissoa ulve 
and R. subumbilicata, and of the second R. parva. These are 
true littoral Rissoe. Many minute shells which conchologically 
appear Aissoe inhabit only the corallie zones, and as most of 
the animals are unknown, the true relations between the ani- 
mals of the littoral and coralline districts are not as yet satisfac- 
torily ascertained. 
Litiorina has only four species, L. littorea, L. rudis, L. neri- 
toides, and L. littoralis. 
I now proceed to the specific descriptions :— 
Assiminia, Gray and Leach. 
Assiminia Grayana. 
Animal spiral, yellowish brown; mantle simple; head with a 
