274 CRETACEOUS GASTROPODA 
A. Barleeia, Clark, (Gen. I, p. 322). 
5. Fairbankia, Blanford, (Ann. Mag. Nat. Hist. for 1868.) This genus has 
been lately proposed for a species from the Bombay Coast, F. Bombayana, BIf. 
The shell is conically elongated like a Rissoina, of moderate thickness, covered 
with a brown epidermis and with numerous spiral strie; aperture ovate, internally 
smooth, anteriorly roundish, edge of the outer margin sharp, but externally thickened 
into a distinct varix. Operculum thin, horny, sub-annular, with a lateral nucleus near 
the middle of the internal edge, and provided on the interior side with a raised rib. 
The form of the animal agrees with that of true Rissoe. 
The greater thickness of the shell and the external varix of the labrum in 
Fouirbankia principally distinguish it from Barleeia. Forbes and Hanley (Moll. ITT, 
p- 120,) say that the shell of Rissoa (Barleeia) rubra is quite smooth, while 
H. and A. Adams, (Gen. I, p. 332,) record a spiral striation. The operculum of 
Barleeia is stated to be interiorly testaceous, with a raised rib and an apophysis 
which projects from the nucleus, while in Fairbankia the operculum is thin, horny, 
internally with a raised rib, but without an apophysis. It is evident from this, that 
both the last named genera are closely allied, but still in some respects so character- 
istically different, as to be able to be generically distinguished. Gray (Guide, 1857, 
p. 111) proposes for Barleeia a distinct family, apparently chiefly on account of 
the existence of a testaceous operculum. This separation is, however, hardly 
necessary, for we have a number of other similar instances of difference in the 
operenla, as in the BrrainiivZ, HYDROBIIN#, and others. 
6. Fenella, A. Adams, 1860, (Ann. Mag. VI, p. 336,) is a pupoid form of 
Rissoa with spiral and transverse ribbings, but the outer lip without a varix. 
7. Mohrensternia, Stoliczka, 1868.—Next in the series, with respect to the 
structure of the shell, appear to follow those fossil species of the rzssozva#, which 
Schwartz von Mohrenstern pointed out in his Monograph of Rissoa, p. 12 (Denksch. 
Akad., Wien, 1864, Vol. XXIII, pt. II,) as forming a separate section of that 
genus, like &. angulata, Hich., R. imflata, Andrz. and others; they occur in the 
brackish or fresh-water deposits of central and eastern Europe. The characters 
of the genus may be described as follows— 
Mohr. testa turriculata, tenwi, semipellucida ; anfractibus sepissime transver- 
saliter costulatis ; columella ad basin aliquantisper fissurata; apertura subovata, 
postice angulata, antice rotundata ; marginibus interdum, (precipue antice) paulo 
dilatatis ; labio intus levi, labro extus haud varicoso, simplict. 
Operculum atque animal incognitum. 
In a quantity of sand, which I received from the Arakan Coast, were a 
number of shells, which extremely resemble the fossil species of Mohrensternia, 
but they were all dead specimens without opercula and with the surface partially 
worn off, which makes it somewhat doubtful whether they belong to this genus, 
for such forms could possibly be imperfect specimens of Alaba. 
8. Onoba, H. and A. Adams, 1854, (Gen. I, p. 331). Shell of moderate 
thickness, partially covered with transverse ribbings; margins of the aperture 
