OF SOUTHERN INDIA. 35 
gives the shell a form very much resembling the point of an arrow. Prof. Forbes 
(loc. cit.) attributed the formation of the callosity solely to the outer lip, which is 
not strictly the case. In Forbes’ figure also the anterior extremity of the last whorl 
is probably more restored than the actual specimen seems to allow. Only further 
and better collections of specimens can clear up the doubt existing on these questions. 
Localities. 8. of Serdamungalum in the Trichinopoly group, out of a. blueish 
calcareous sandstone very similar to that near Pondicherry, wherefrom Prof. Forbes’ 
specimens were procured. 8. W. of Mulloor, Arrialoor, N. of Olapaudy, W. and 
S. E. of Karapaudy, in the Arrialoor group, out of a light-coloured, often somewhat 
siliceous or ferruginous sandstone. 
Lormation. Trichinopoly and Axrialoor groups; more common in the latter, 
V. PTERODONTA, D’ Orbigny, 1843. 
Tynostoma, Sharpe, 1849. Quart. Journ. Geol. Soc. Lond. Vol. V, p. 376. 
VARIGERA,* D’Orbigny, 1850. Prodrome, Vol. II, p. 103. 
Pier. testa ovato-elongata, crassa, superficie levigata interdumque polita; spira 
conica sew turritellari; ultimo anfractu subventricoso seu inflato; apertura ovali, 
intus levi atque callosa, antice emarginata seu canaliculata; labro parwn dilatato, 
mtegro, intus ad marginem aperture denti-seu varici-forme incrassato, dentibus uc vari- 
cibus in anfractibus junioribus ad intervalla sepissime preservatis. 
So many different opinions had been already pronounced upon the nature of the 
fossils, which we unite under the above name, that we cannot pass over this subject 
without entering briefly on the history of these shells. At the same time it will be 
necessary to state the reasons which have induced us to regard two genera, univer- 
sally believed to be totally distinct, as synonymous. Our remarks will, we trust, 
also show the necessity of classing the genus Pterodonta, as here characterized, in 
the immediate vicinity of the typical Rostellarie. 
* Although there cannot in reality be very much doubt, that D’Orbigny under his Varigera meant gene- 
rically the same shells for which Sharpe proposed the name Tylostoma, still it is surprising, that no French 
paleontologist who has access to any of D’Orbigny’s original specimens has thought it worth while to inspect 
the same and settle every doubt on this point by the publication of a few lines. If anybody reads D’Orbigny’s 
characteristics of Varigera (Prodrome, II. p. 103), he cannot help thinking, that D’Orbigny meant under his 
“varices longitudinales” eaternal varices on the shell, for he does not even hint, that the specimens which he 
examined, were casts. Moreover, on page 68 ibid., he says of Var. Ricordeana, “espece oblongue a fortes 
varices sur une surface lisse.” Farther, he compares the varices of Varigera with those of Scarabeus. The fact 
is, that Scarabeeus has very often remains of the margin of the outer lip placed externally on opposite sides, 
but these remainders are very thin and wear very soon away. I am, however, not aware of any such external 
traces of the margin of the aperture in any of the species, which have been described as Pterodonta or Tylostoma. 
If D’Orbigny had only cast-specimens before him, and if he meant by his varices impressions of the same; or 
if it can be supposed, that he understood these varices to be internal, his characteristics immediately become 
more intelligible; but who can reasonably presume on such essential alterations in the characteristics of a 
shell? The comparison of the last internal varix of Pterodonta with the internal varix near the margin of the 
outer lip, before it expands, in Scarabceus is perfectly correct ; there could not be possibly a better comparison 
selected. It must, however, be remembered, that this varix is absorbed on the preceding whorls and only exists 
near each renewed apertural margin. There is, therefore, only one varix in Scarabeus, not several as in 
Pierodonta ! 
