OF SOUTHERN INDIA. 381 
subspiral nucleus. Judging from the very great similarity (if not generic identity ?) 
of the shells of Scisswrella and Pleurotomaria, it appears very probable that the 
animals were also similarly formed. 
The shells of the Pruvroromarripm are more or less conically elevated, turreted 
or trochiform, with a slit or a number of perforations in the outer lip. 
The recent Sciswrelie are said not to possess an internal pearly layer, but the 
recent Pleurotomaria Adansoniana and some of the fossil species (as for instance 
those from the Russian jurassic deposits near Moskau) appear to be pearly within. 
It seems to me that the pearly layer of the minute Scisswrelle is only very thin, 
so as to be hardly noticed in the transparent shells. I am sorry that I have no 
fresh specimens to examine. The genera which appear to constitute this family, 
as known at present, are the following :— 
1. MMurchisonia, V@ Arch. et de Verneuil, 1841. Shell turreted, aperture ovate, 
entire in front, outer lip with a short slit, being in connection with a distinct band, 
traceable on all the whorls. The species are all paleeozoic and offer a great variety 
in form. An internal pearly structure has not been observed. 
2. Forskalia, H. and A. Adams, 1855 (Gen. I, p. 482). Shell turbinate 
or subconic, plicated at the sutures, along the anterior of which a narrow band 
exists, outer lip with a very short emargination. The type of this genus is 
Forsk. fanula, Gmel. H. and A. Adams place it as a sub-genus of Gibbula; but 
judging from the analogy in the form of the shell, the genus must be placed in 
the Pzrxvrorowarups#, and I think Ryckholt is quite correct in stating that 
the Trochus fanulus (Forskalia id.) is quite as closely allied to Pleurotomaria, 
as is Subemarginula to Emarginula (vide Journ. de Conch., 1860, IV, p. 184). 
There are indeed a number of palzeozoic species, like Pl. contraria, Pl. Galeottiana, 
Pl. inflata, and others of Koninck, and of mesozoic species like Pl. monilifera, 
@’Orb., which can with great difficulty be distinguished from the recent Forskalia. 
3. Porcellia, Leveillé, 1835. Shell symmetrically discoid, with a narrow 
band on or near the centre line of the back, corresponding with a slit on the outer 
lip of the aperture. The species are paleeozoic and lower secondary. Hérnes 
properly remarks that the genus can be retained only for the symmetrically 
discoid forms, for it cannot be questioned that some of the jurassic subdiscoid 
Pleurotomarie (like the Pl. mirabilis, Desl. and Pl. platyspira, d’Orb., from 
Normandy) are very closely allied in form, but they are always distinguished by a 
broader band which is not quite centrally placed. 
4. Pleurotomaria, Defr., 1821; shell broadly conical, pearly within, slit in the 
outer lip moderately deep, band rather broad, inner lip of the aperture slightly 
thickened, columella solid or hollow. Species of Pleurotomaria occur through 
all the sedimentary deposits from the Silurian upwards. Tertiary species are very 
rare, and only two, Pl. Quoyana and Adansoniana, have been found recent. 
I fully agree in the statement of Eugéne Deslongchamps that a generic 
(or sub-generic as it may be called) sub-division of the species usually determined 
as Pleurotomaria is very desirable (Bull. Soc. Linné. Norm., 1865, vol. TX, p. 422). 
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