154 CRETACEOUS GASTROPODA 
Locality.—Coonum, Andoor, 8. of Serdamungalum, and Kolakonuttom, in the 
Trichinopoly group; not common. 
Lormation.—Trichinopoly group. 
3.—RAPA CANCELLATA, Sowerby, sp. Pl. XII, Figs. 12—16, & Pl. XIII, Figs. 1—4. 
1846. Pyrulacancellata, Sow., Forbes, Trans. Geol. Soc. Lond., VII, p. 128, Pl. XV, Fig. 12. 
1850. Lusus Forbesianus, D’Orb. Prodrome, II, p. 229; idem Pictet, Gabb., and others. 
R. testa ventricosa ; spira brevi; anfractibus quinis, postice applanatis sew lente 
excavatis ; ultimo ad peripheriam bicarinato : carina superiori acuta, fortiori, inferiori 
nonnunquam obsoleta ; canali contorto, aperture marginem exteriorem versus curvato ; 
columella plus minusve excavata; superficie striis spiralibus granulosis ornata, 
nonnullis minoribus, alteris prope suturam atque in carinis fortioribus ; apertura elon= 
gata; canals aperto ; labio calloso, antice applanato ; labro in etate juniors tenui, ad 
marginem intus sulcato, in etate provectiori mcrassato, obsolete sulcato. 
The form of this species is rather variable, as may be seen upon a view of the 
figures given on Plates XII and XIII. The spire of the shell is always very short, 
the last whorl ventricose, and above, like all the previous, flattened or even 
slightly excavated. On the periphery there are usually two keels present, the upper 
one being much stronger, and the lower becoming occasionally obsolete in more fully 
erown shells. The entire surface is covered with granulated spiral strie, those near 
the suture and on the keels being much stronger. Sometimes the transverse ribbings 
form stronger tuberculations on the peripherical keels, while the other spiral strize 
are comparatively much thinner. 
The aperture is angularly elongated; the posterior canal is slight, but always 
distinctly marked. As in the typical, living, Rapa papyracea the anterior canal is in 
young specimens proportionally much longer than in old ones. It is not perfectly 
preserved in any of our numerous specimens, but in Fig. 12, Pl. XIT, it is nearly 
complete. From this it was evidently somewhat contorted and bent back towards 
the outer margin of the aperture. The inner lip is considerably thickened, smooth, 
anteriorly flattened, covering with its margin the termination of the columella 
sometimes perfectly, or leaving it widely open. The outer margin is thin and 
internally sulcated in young specimens (Figs. 18 and 14, Pl. XII), while in full 
srowth it is much thickened (Fig. 1, Pl. XIII). 
The specimen figured by Forbes was no doubt partially a cast, and his descrip- 
tion must have been derived from other better preserved individuals; the lower 
peripherical keel seems to have been not much developed, and on casts it is actually 
scarcely traceable. From some specimens in the Madras Museum there can be 
little doubt that Sowerby and Forbes had the fossil, as here specified, under consider- 
ation. It is one of the most common species, and tolerably well characteristic for 
the Trichinopoly group. 
