130 CRETACEOUS GASTROPODA 
The specimen under description is rather imperfect, neither the apex nor the 
aperture is preserved, but the very characteristic ornamentation may for the present 
serve as a sufficient distinction. The inner lip is thin and smooth; near the suture 
the shell is remarkably solid. 
Locality.—S. of Serdamungalum in Trichinopoly district ; apparently very rare ; 
only the figured specimen has been examined. 
Formation.—Trichinopoly group. 
XI. Family —TRITONIIDZ. 
Animal with a thickened, truncate head; tentacles of moderate length, with 
the eyes on the external thickened basis, or within the first half of their length; 
proboscis long, retractile; lingual membrane, with teeth in seven rows, the lateral 
in three series each; mantle enclosed; siphon usually produced and nearly straight ; 
foot always expanded, with thin margins, truncate anteriorly. 
Operculum ovate, lamellar, of the same size as, or occasionally smaller than, 
the aperture, and with an apical or lateral nucleus. 
The shells are more or less ovate, usually thick and consistent, covered with a 
rough, horny epidermis ; the whorls ornamented in the course of growth with per- 
manent apertural varices, of which at least the last one is always distinguished, even 
when all the previous become obsolete ; the surface is usually roughly covered with 
spiral strie and more or less spinose tubercles ; the aperture is ovate and both lips 
usually denticulated or sulcated; the inner lip has often posteriorly an elongated 
tooth so as ta narrow by it the aperture ; the canal is more or less produced. 
The genera usually admitted in this family are Ranella (Bursa, Adams, Apollon, 
Gray) Persona (Distortio, Adams), and Tritonium, of the first and last of which 
H. and A. Adams quote a number of sub-genera. Gray restricted the name Ranella 
for R.crumena (and 2), as distinguished by a semiovate operculum, with a centro-lateral 
nucleus, and places it in the Casszpzm (Guide, 1857, p. 39). If this be admitted, 
Persona in having a similar operculum and differing far more in the constitution 
of the shell must be separated from the Trzronmp# also. There does not seem any 
particular necessity for either change, as otherwise nearly the entire family must be 
disbanded. 
A generic distinction of those species, as R. crumena, within the family 
Trrrovips, appears quite sufficient. It cannot be questioned that the present dis- 
tinction, as accepted between Ranella and Tritoniwm, based principally upon the 
number of varices in one whorl, is very uncertain. When Philippi searched anxi- 
ously after other distinctive characters between Ranella and Tritonium, it shows 
only that he had carefully observed a number of one and the same species in 
different stages of growth. For if any body has had the opportunity of examining 
a really large number of these living shells on the sea-coast, he will easily be con- 
vinced, that he could make a good number of species of Tritoniwm and Ranella 
