OF SOUTHERN INDIA. 259 
XXIX. LFumily,—PLANAXIDA. 
(Sub-families,—PLANAXINA] and LITIOPIN 4). 
H. and A. Adams’ Genera, I, p. 321; Gray’s Guide, 1857, p. 95 ; Chenu’s Manuel, Zrrorrip-7 
in parte, p. 303, 
Judging from the accounts given by H. and A. Adams and Gray of the 
position and form of the gills and of the existence of a distinct siphonal fold, the 
separation of these shells from those of the Zzrorrvipx% appears justifiable, 
although the animals and shells of both of them are in many other respects very 
much alike. On account of this similarity we would prefer to range the Pravaxrp» 
in this place, rather than after the Czrrrazzpx, to which some authors have referred 
the genus Planavis. 
The family could be divided conveniently into two sub-families, pzavaxrve and 
zitiopiIn®, with the genera Planaxis and Litiopa as the respective types. The 
species belonging to the zrrroprvx are mostly thin shells, and in the same sub-family 
have to be classed all the species of Alaba, which A. Adams separates into three 
sub-generic groups, Alaba, Diala, and Styliferina (vide Ann. Mag. Nat. Hist., 
1862, X, p. 294). 
Although the species of Lirorrwip# and similar forms already begin in the Silurian beds, there 
are no certain remains of the PLavaxro# as yet known below the tertiary strata, and even from 
these only very few have been reported. 
XXX. Fumily,—LITORINIDZ.. 
H. and A. Adams’ Genera, I, p. 812; Gray’s Guide, 1857, p. 86, and LACUNIDZ, p, 92; 
Deshayes, Anim. s. vert., Foss. de Paris, 2me. edit., Vol. II, p. 355. 
Theanimals of the Zzrorrmrpx have a moderately expanded foot, adapted for 
walking or sliding on rocks; the mantle is generally enclosed with an entire edge, 
or occasionally with a rudimentary siphonal fold in front. The rostrum is produced, 
wrinkled, and not retractile; jaws horny ; lingual ribbon with one central and three 
lateral teeth on each side; tentacles lengthened, subulate, far apart on the head, with 
eyes sessile, or on small bulgings near their outer base, or situated within the length - 
of the tentacles; usually without neck-lobes or lateral cirrhi; operculigerous lobe 
simple, seldom provided with appendages, or perceptibly expanded. The gills are very 
large, formed of numerous flat, free plates and occupying nearly the whole surface of 
the branchial cavity. ‘The pectinations of the branchial plume of some Zzrorzwrp.2z 
are, however, stated to be so fine and slender, as to be occasionally scarcely notice- 
able. Gray calls them, therefore, PsEUDOPNEUMA, adding the Teuyearenzrp# to 
them. It seems in fact, that the division of the branchial plume into numerous 
pectinations precedes the total disappearance of the gills, for the branchial plumes 
seem to become gradually more slender and finer in those animals, which are 
found in places high above the low tide mark. Several species thus seem actually 
