352 LITTORINID As. 
exclusively confined to that genus, and which must, I think, 
fix the Lacune of authors for ever as one of its sections. 
With regard to the aid derived from the tongues of the 
Gasteropoda for generic or specific distinction, I am inclined 
to think its importance overrated, because no two species of 
the same genus have a precisely similar disposition of the 
rachis, uncini, and arrangement of the spines and inter- 
weavings of the lingual riband. This fact sets at rest generic 
views; the tongues, at best, are of mere specific value. I 
have examined hundreds, and can make nothing of them that 
can at all be depended on, from their extremely variable struc- 
tures. The tongues of great numbers of the minor species 
cannot without extreme difficulty be obtaimed by the scalpel ; 
they can only be detected after maceration, and compression 
under a powerful microscope, and the comparison of these 
minute species is attended with difficulties and very unsa- 
tisfactory results. The ootheca of the Mollusca may be useful 
in comparison, if they can be obtained, and identified to be- 
long to certain species. 
I conclude, and insist on the foregoing positions, with as 
much tenacity as courtesy will allow to the phrase. I cannot 
even consent that the Lacune be considered a subgenus of 
the Littorine. I think the term subgenus an unsatisfactory 
and hybrid expedient to attempt to express an intermediate 
state that does not exist; with me, subgenera are resolved 
either into distimct species or genera. If I might consider 
that those who use the term subgenus mean to define it as an 
ageregation of particular or aberrant species of a distinct 
genus, | would accept the definition, but not the term, which 
ought to be section, as that of subgenus seems to imply 
something beyond divisional arrangement. 
The Littorina puteolus with us, and its congener L. vincta, 
though examined, are not described. The Littorina crassior 
we have not seen. 
LitTToRINA PUTEOLUS, nobis. 
Lacuna puteolus, Turton. 
» Brit. Moll. iu. p. 58, pl. 72. f. 7, 8, 9; pl. 74. f. 9. 
