350 LITTORINID A. 
canal of the sac that contains the viscous fluid. The neck of 
the animal is simple and free from membranous lappets, as is 
the case in all the Littorine. The fecal pellets are elongated, 
slender, subcylindrical, having the apices tipped with a dark 
hue. The verge is a long, simple, arcuated, flattish, pale 
yellow process, regularly tapering from its insertion under 
the right tentaculum to a fine pomt. The operculum is pale 
horn-colour, subelliptic; nucleus excentric, sublateral, abut- 
ting on the columella, with 24 volutions, the last of which 
rapidly unites with the margin. We repeat the remark on 
the internal organs of the Littorina littoralis, in comparison 
with this species, that they are identical. 
Malacologists will observe, that in the two species the 
internal and external organs are essentially the same; the 
only variations are, that in Littorina pallidula, the caudal 
filaments, the expansions of the operculigerous lobe, and the 
form of the organe générateur, are not precisely similar to the 
parts in L. littoralis. The former are very variable specialties 
and cannot be depended on: ev. gr. the Lacuna puteolus of 
authors is without caudal processes, or at least they are obso- 
lete ; the same observation may be made of the Rissoe, no 
two animals of the same species being similar in respect of 
caudal accessories, and many are without them. The male 
organs of the two undoubtedly vary in structure; the groove 
or lacuna in the pillar, from whence the generic title, is a 
mere modification of the umbilicus, which, from its variable- 
_ ness, is not of specific value, and is quite misapplied to generic 
determination. All the variations we have mentioned are 
specialties of slight consideration, which cannot be put in 
competition with the essential generic characters of the foot, 
and its singular plan of locomotion, which stamp the so- 
called Lacune of authors as genuine members of the genus 
Littorina. 
Since the above was written, I have reviewed, in a living 
state, all the Lacune of authors, except the “ crassior,” and I 
think I am authorized to be still more “ tenax propositi,” that 
they are a section of the genus Littorina, and cannot be 
severed from it without violence to true generic value. I find 
