OF SOUTHERN INDIA. 39 
of this varix or tubercle to an accidental secretion; upon this we, of course, 
cannot pronounce any opinion, not being in possession of any specimens of this 
very rare shell. The similarity of the interior varix to that of Pterodonta must, 
however, strike every observer, and we wish, therefore, to draw special attention to 
this fact. Subsequent researches will, it is to be hoped, throw some more light upon 
this ‘accidental secretion.’ As the varix in R. Dewalquei is placed near the edge of 
a, greatly expanded outer lip, it is a matter of course, that no trace of its existence 
could remain preserved on the previous whorls. The distinction of this species 
from a Péerodonta is, therefore, quite evident; still the presence of the tooth offers 
some analogy. 
From all these remarks it is, we trust, tolerably certain, that Tylostoma and 
Pterodonta are identical forms, which must be classed in the family Azar. Still 
on the other hand it cannot be denied, that the discovery of new and better materials 
may call for several changes, and perhaps even sub-divisions, in the genus at 
present known as Péerodonta. I would consider the following point only as one of 
these probable changes. 
Pictet described in his “ Fossiles des Grés verts,” p. 265, Pl. 26, Figs. 1 and 2, 
two species Pterodonta gaultina and Pt. carinella, both of which differ from 
D’Orbigny’s typical Pterodonta and the species of Tylostoma by their elongated 
fusiform shell, provided apparently with a long straight canal, but still with internal 
varices or tubercles on the outer lip, leaving at certain intervals impressions on the 
casts of the shells. On account of the produced canal M. D’Orbigny referred these 
two species to Pterocera (Prod. II., p. 132), having then changed his original idea 
about Pterodonta and believing in its relation to Act@on. M. Pictet at first agreed 
with these changes (vide Gres verts, p. 549), but lately (Mat. Pal. Suisse, 3me. ser. 
p. 626) he refers the Pé. gaultina to Aporrhais, and (ibid. p. 657) the Per. carinella 
to Murex. There have not been any better preserved specimens of these species 
found, and M. Pictet says, that he considers these changes only as provisional. It 
would not be in the least surprising, if further materials would show the close rela- 
tionship of these species to Péerodonta and confirm in this way /Picte?’s original 
determinations. I think it very likely that this may be the case. 
Seeley described (Ann. Mag. Nat. Hist. ser. III, Vol. VII, p. 282—283) from the 
upper Greensand of Cambridge two species Pterodonta marginata and Pt. longis- 
pira. Both are known from casts only, on which, however, the beginning of an expanded 
outer lip, similar to Alaria or Aporrhais, is distinctly traceable. The upper whorls 
are ribbed transversally, and there appears to be a strong impression of an internal 
tooth or tubercle near the aperture. These tubercles are placed below the median 
keel, where in other species there is always some kind of an insinuation and con- 
traction of the aperture, generally caused by a thickening of the outer lip. No 
trace of these tubercles has been as yet observed on the whorls of the spire. Should, 
however, these two species be proved to belong to Pterodonta, they must be classed 
with the two last named species of Pictet in the same section. A fifth species, which 
belongs to this same division of fusiform Pterodonte, is figured on our Pl. V, 
