OF SOUTHERN INDIA. 293 
lip of Zyl. naticoides is not a generic character, for we have often seen it in other 
species not more callous, as for instance in Amp. sortita, (see figures of the species 
on Pl. V). 
All these characters, combined with the strong and smooth shell, are not 
opposed to the classification of this genus in the NMazrcrpz, but on account of the 
internally thickened outer margin, we would suggest to distinguish these shells as a 
separate sub-family. There is no other family in which they could be better placed, 
as already correctly pointed out by Sharpe, D’Orbigny, Morris, a. oth. The internal 
varices are not always present on the upper whorls (as stated on p. 37), and 
in such cases the distinction between imperfect specimens of Tylostoma and 
Ampullina or Huspira is extremely difficult, or sometimes actually impossible. 
When the internal varix of the outer lip is toothed or crenulated, no better 
comparison can be made, than that between the shape of the aperture of Tylostoma 
and that of Scarabus, Montf. (vide p. 35). The peculiarly punctated surface of 
the shell in some of the species, is quite similar to that of many other Narre, 
smooth species of Azara, and others. 
With reference to the structure and other characters of the shell of Tylostoma, 
I must direct the reader to my previous observations on pp. 35-41. I have only 
to state what I at the present consider to be the distinctions of Pterodonta from 
Tylostoma, and in what way the large number of known species ought to be 
classified. 
First I may remark, that D’Orbigny’s Varigera, (of which I said, p. 35, that 
the author’s generic characteristics were not clearly defined), is unquestionably 
identical with Tylostoma. D’Orbigny makes reference to external varices, and 
these are indeed sometimes present, as I previously suspected, (see note on p. 35). 
They are produced by the remains of the somewhat dilated margin of the outer lip, 
as the shell grows larger. Generally, though not constantly, these varices are 
opposite, being distant half a whorl from each other. In many species there is, 
however, not a trace of them to be found, and therefore their appearance cannot 
be considered as of generic value. 
Sharpe’s original specimens of Tylostoma are now in the collection of the Geol. 
Society of London; they all belong to that genus, though many of them are very 
imperfect. 
D’Orbigny made no correct distinction between his Pterodonta and his 
Varigera, either in the Paléont. francaise, or in the Prodrome. Of the three 
species, described by that author in the former publication, Pé. inflata must 
most probably be transferred to Tylostoma; the two others belong to Pterodonta. 
The Pt. naticoides is certainly a typical Tylostoma, but all the other species of 
D’Orbigny’s Pterodonta and Varigera are represented in his collection by such 
very indistinct casts, that I would not venture to pronounce anything certain 
even with regard to their generic, much less with regard to their specific 
determination. Most of the species described by Pictet and Coquand correctly 
belong to Tylostoma. 
4c 
