360 LITTORINIDA. 
tum, I need only quote the learned authors of the ‘ British 
Mollusca,’ who, speaking of the Rissoa striatula, remark, 
“The animal of this, as of too many other Rissoe, is yet 
unknown.” 
I have reviewed, at Exmouth, the several species already 
alluded to, and added some new ones; I may therefore speak 
with increased confidence of their descriptive accuracy as far 
as regards the external organs, but I apprehend that a correct 
anatomy of such minute creatures is a vain expectation; we 
must therefore rely on analogy, for at least the general 
characters of their terior organization. 
It is necessary to mention that the almost microscopic 
organs of these diminutive species require the aid of good 
glasses to see their true forms and attributes; the present 
descriptions are the result of the organs being viewed through 
Coddington lenses of as high powers as were consistent with 
distinctness: inferior means give false appearances, and are 
often the cause of discrepancies between observers of the same 
animal. 
R. striata, Montagu. 
R. striata, Brit. Moll. ii. p. 94, pl. 78. f. 8, 9. 
Animal inhabiting a white shell of 5-6 rather tumid, semi- 
plicated, spirally striated volutions ; it is hyaline-white im most 
parts; an exception is the upper and under surface of the 
rostrum and buccal fissure, which are of a sordid lght red- 
brown. Mantle even with the shell, except that a minute 
eirrhal filament, very difficult to be seen, issues from it at the 
upper angle of the aperture, as in the type R. parva, in which 
it is never absent. 
The head is a long flat muzzle, deeply grooved above and 
below, with minute lappets on the upper surface near its 
termination, and on the march is carried a little mm advance 
of the foot. The tentacula are moderately long, divergent, 
strong, but flattened, very little setose ; they do not attenuate 
to points like the type, but are of the same breadth throughout, 
and of opake snow-white; in progression they are extended 
considerably beyond the head. The eyes are conspicuously 
black, and placed on minute, scarcely projecting, external 
