346 LITTORINIDA. 
organs are nearly those of L. littorea. The sexes are distinct 
in all the Pectinibranchiata*. I ought to have mentioned 
the suboval corneous dark operculum, pointed superiorly with 
about two rapidly increasing gyrations, the nucleus being at 
the basal end. 
This species is one of those that mhabit the highest levels 
of the littoral zone, and often dwells for an indefinite time far 
beyond even the spray of the sea. It appears a mystery how 
the branchie are kept moist: I suspect the minute saline 
particles carried by the winds suffice, especially as the long 
exposure to atmospheric influences has almost rendered the 
branchiz of pulmoniferous quality. They clothe the rocks m 
myriads on the South Devon coasts. I sum up, and conclude 
the present species to be a true Littorina. 
I mentioned above, that I was preparing further observa- 
tions on that branch of the Littormidan family which is termed 
Lacuna, and that I had reserved the description of the Litto- 
rina littoralis as a standard of comparison with its animals : 
T also stated my opinion, that they ought to merge in Litto- 
rina as species. I now present notes thereon, which I beg 
may be considered the sequence and termination of my former 
observations, and which, with the addenda, will render them 
nearly complete. These notes are the result of an examina- 
tion and comparison of many living examples of the Littorina 
littoralis and the Lacuna pallidula of authors, which latter 
species, with me, will now be the type of a section of the Lit- 
toring, as | am confirmed in my views that the genus Lacuna 
is superfluous, and its species ought to pass to Littorina. 
My remarks embrace the Littorina vincta, “puteolus” and 
“ crassior,’ which, with the LZ. pallidula, clude all the varie- 
ties of the Lacune of authors. I am inclined to think I have 
named more species than really exist, and that they may be 
reduced to three, the “ crassior”’ being considered, when de- 
nuded of the epidermal laminze, a strong, elongated, smooth, 
* Since this was written I have found reason to doubt this conclusion, 
as will appear hereafter. 
