348 LITTORINID 4. 
the aspect of having a narrow upper lobe separated from the 
pedal disk, forming a pair of narrow labia ; the upper posterior 
portion of the operculigerous membrane in this species is 
very slightly expanded laterally, and though not emarginate 
with caudal appendages, as in Littorina pallidula, is often 
sinuated and sometimes finely cloven. The operculum is 
nearly the shape of a vertical section of a pear, brown horn- 
colour; nucleus sublateral, leanmg on the columella, with 
about 24 gyrations, the last of which rapidly coalesces with 
the outer margin of the plate. The animal has the true alter- 
nate undulatory longitudinal characteristic progression of the 
Littorine. The neck is simple, without lobes. The branchial 
plume is single, on the left side, with 35-40 or more very fine 
long close-set pectinations, many of which in certain positions 
of the animal may be seen under the mantle without dissec- 
tion. The orifice of the anus and the canal of the sac of 
viscosity are seen on the right side; in the female the matrix 
and its orifice, with the anterior part of the ovary, and in the 
male, the verge. The fecal pellets are pale red and exactly 
oviform: I allude to this point, as I have sometimes found it 
a good distinctive aid. 
T have mentioned rather more than can be seen without 
dissection ; and I will only enter so far on the anatomy of 
this species as to observe, that I have carefully compared 
numerous specimens of the L. littorea, L. pallidula and L. ht- 
toralis, and I can pronounce all the internal organs, including 
the cesophageal ganglia, to be absolutely identical, allowing 
for the modifications of colour in the different species. The 
male organe générateur supplies the position of the matrix in 
the female, and the testis that of the ovary; the former springs 
under the right tentaculum, and is composed of two portions, 
the basal one bemg a tumid, annulated or rigid figure, den- 
tated exteriorly, with the minute orifice at the external angle ; 
the other angle is produced into a yellow, conical, arcuated, 
pointed, rather long process, the only use of which would 
appear to be that of an organe excitateur. 
