Mr. W. Clark on the Littorinide. 359 
variety from locality, varying in number and in the inflation of 
the volutions, and in colour from pale brown or yellowish white 
to dark red-brown or horn-colour. I think that one of the light 
varieties with the tumid volutions is Montagu’s Turbo subumbi- 
licatus, which species appears to be in great obscurity. Having 
carefully examined the animals of all the varieties, I can decidedly 
state that they are identical with the typical Rissoa ulve. I am 
much inclined to think that the Rissoa Barleei is one of the 
varieties. 
‘ Rissoa, Fréminville. 
Rissoa parva, Mont. et auctorum, 
R. costulata. 
R. rufilabris. 
R. scalariformis. 
R. interrupta, §c. 
Animal spiral ; mantle plain, just even with the shell; the head 
is a short dark brown muzzle, cloven with a vertical orifice be- 
neath, the disk of which is yellow; tentacula long, slender and 
cylindrical, yellow, with a longitudinal row of white detached 
flakes, and often the reverse, white, with yellow imterrupted 
flakes ; eyes on short offsets at the external bases. Foot flaky- 
white above and beneath, long, narrow, truncate in front, slightly 
auricled ; the point is blunt, from whence a small upper lobe or 
membrane springs, on which is fixed a suboval corneous oper- 
culum with spiral loose striz, and at its extremity a single short 
white tentacular filament is seen. The branchial plume consists 
of 15-18 minute vessels attached under and to the mantle and 
back of the neck. 
This is another of the genera the conchologists have taken 
possession of for the manufacture of varieties into species. The 
type Rissoa parva is a most variable species, resulting from loca- 
lity and other causes. The animals of all the varieties enume- 
rated above are identical; we have examined them all, and can 
find no appreciable difference except varieties of colour and oe- 
casional variations in the length of the terminal filament, which 
is never in any two selected shells precisely similar. The R. 
costulata is an elongated variety; the R. rufilabris a short 
tumid one, with a red or pink peristome, which may often be 
seen in its congeners. The R. interrupta is a more slender, thin, 
less plicated, dwarf variety. The R. scalariformis has the plice 
more numerous, white and delicate ; and lastly, the typical Rissoa 
parva varies so much that it is difficult to find two shells alike. 
These varieties live in company in the lower levels of the littoral 
zone, but are more plentiful at the borders of the laminarian 
district. 
