260 CRETACEOUS GASTROPODA 
for weeks together to live only in the moist air on the sea coasts,* and in these 
species the gills are said to be very rudimentary. A few species live in fresh or 
brackish waters. 
Operculum horny, multispiral, with nearly central nucleus; or pucispiral, 
with a lateral or subterminal nucleus. 
Shell spiral, conical, with more or less turbinate or depressed spire; aperture 
ovate, anteriorly entire or obsoletely effuse, internally never pearly. 
The number of genera, which are admitted by different authors in this family, 
is very variable. Having adopted Gray’s and H. and A. Adams’ views as regards 
the family Pravaxipm™, we would in a similar manner suggest a division of the 
Lirrorryip& into the three sub-families, ross4riINZ, LACUNINE and LITTORININA. 
a. Sub-family,—PFOSSARIN 4.~ 
Shell solid, spire depressed or short, last whorl ventricose, columella usually 
hollowed out; aperture anteriorly sub-effuse ; surface ornamented with spiral and 
transverse ribbings or stri@. 
This group may include the following genera :— 
1. Risella, Gray, 1840, showing by its broad, conical form great relation to 
the Sorarmp#. 
2. Fossar,t Gray, 1840, (Syn. Brit. Foss.;—H. and A. Adams’ Genera, I, 
p. 819); this genus has been separated by Recluz (Jour. Conch., XII, p. 247) 
into two. For those species, which have the mantle margin entire and a kind of 
veil between the two tentacles, the name Fossar has been retained, while the name 
3. Clathrella, Recluz, 1864, has been proposed for those species, which have 
the margin of the mantle crenulated, but not possessing a veil between the 
tentacles. The shells of both these genera are very similar. 
4. Fossarina, Adams and Angas, 1863, (Proc. Zool. Soc., p. 423); the type 
is Fossar variegatus, Ad. 
5. Isapis, H. and A. Adams, 1854, (Gen. I, p. 320). The shell is distin- 
guished from Fossar by a central tooth on the inner lip, resembling that of Nati- 
codon of Ryckholt (Fam. Nzerrropsrp£). 
6. Conradia, A. Adams, 1860, (Ann. Mag. Nat. Hist., V, p. 409), a genus 
somewhat intermediate between Trichotropis and Fossar; it much recalls the fossil 
Purpurina. A. Adams (Proc. Zool. Soc., 1868, p. 110) proposes in this genus two 
sub-genera, G'ottoina and Cithna; the shells are from the Japan seas. 
* Of many of the species of Lnttorina a large number of specimens can often be found together, attached 
to rocks above the usual high water mark, where they are hardly springled with water once in a few days. 
They are generally, for the greater part of the day, exposed to the powerful rays of a tropical sun, but they 
attach the aperture of the shell so perfectly air-tight to the rock, that hardly any evaporation of the water 
can take place, and consequently their gills are kept moist. 
+ It is true that the name ‘le Fossa’ was at first used by Adanson in his Hist. etc. du Senegal, 1757, p. 173, 
but it was used by this author only as a specific distinction in the Genus Natica; it was therefore not a generic 
name, and Gray was perfectly correct when he used it first in this sense. I do not see what great barbarism 
there is in this name! Any one may take the liberty of saying the same of Fossarus of Philippi, and change 
it into Fossarius. Such changes of generic names, unless they are evident misprints, cannot be admitted. 
