Mr. W. Clark on the Littorinide. 863 
rocks, when they will at once perceive that they are all identical 
with each other and the type L. rudis, and will afford a practical 
proof that species founded on the characters of the shells are ar- 
tificial and delusive, and that the soft parts must also be consi- 
dered to obtain specific distinction. 
The L. rudis, and all the varieties, are extremely impatient of 
continued immersion in water ; when deposited in basins, the first 
object is to escape therefrom and attach themselves to a dry spot. 
In estuaries, where they are often affused by the fresh water, they 
become, particularly the L. tenebrosa, thin and depauperated in 
their shells ; they are sometimes for weeks deprived of even being 
sprinkled by sea water. Though decided Pectinibranchiata, they 
live in the open air with nearly equal facility as the Pulmonifera ; 
and in reference to this fact, as regards another family, the Cono- 
vuli, there are still malacologists, who, notwithstanding the va- 
luable observations of the Rey. T. Lowe, are not quite satisfied 
that they are pulmoniferous ; we have ourselves attempted to 
corroborate Mr. Lowe’s views, but failed from want of sufficient 
specimens. 
The L. littorea is the only species of this particular form that 
requires, to attain full growth, a regular bi-hodiernal immersion 
in sea water, and to obtain it the bulk of that species live in the 
lower littoral levels ; if they are deprived of it, they become stunted 
and dwarf. 
That variety of the L. rudis which is undoubtedly the L. ju- 
gosa of Montagu varies from quite smooth to highly striated, 
and has even ridged, reflected, spiral volutions, as are repre- 
sented in the figure of Montagu’s ‘ Testacea Britannica ;’ it 
clothes the interstices of rocks on the Devon coasts in myriads ; 
they are rarely or never immersed, as they dwell in the same 
highest littoral levels, in most exposed situations, in hke manner 
as their congeners the L. rudis and L. tenebrosa inhabit the highest 
levels of the sheltered and protected estuaries. They are the 
parents of all the dwarf varieties, the L. patula, L. subsaxatils, 
L. neglecta and L. fabalis, &e. 
As a proof that habitat is the cause of these dwarf varieties of 
the L. rudis, I mention that the L. littorea in company with 
them, at a few yards’ lower level, are small, stunted, and nearly as 
dwarfish. By the favour of Mr. Bean of Scarborough I have 
compared his L. zonaria, L. rudissima, L. neglecta and L. fabalis 
with Devon specimens, and found them identical ; consequently 
I presume the animals are so likewise. 
These so-called species are without exception viviparous. How 
happens this singular coincidence ? how is it that none of them 
follow the plan of the reproduction of the other species? This 1s 
a very significant fact, and is, I think, a strong circumstance, in 
conjunction with the positive similarity of the animals, in favour 
