OF SOUTHERN INDIA. 439 
figures several species, like D. Delesserti, Chenu, and D. grande, Desh., which also 
are type species of this genus. Others are described by Deshayes in his last work 
of the Paris fossils (pl. I and II of vol. II). ‘The posterior end is usually 
longitudinally striated even when these strice or ribbings become obsolete towards 
the aperture, but the principal characteristic of this genus rests in the short and 
wide slit of the ventral or convex side of the posterior end, while the dorsal margin 
is entire or very slightly emarginated. In Dentaliwm (as restricted) the margins 
are either entire or dorso-ventrally slightly indented, so that the distinction is only 
a very gradual one; but as the animals also appear, by the more cylindrical and 
pointed form of the foot, etc., to exhibit some differences, a generic separation seems 
very desirable. The existence or want of the posterior supplementary tube does 
not appear to be of any great generic importance, inasmuch as it is occasionally 
present or wanting in very allied forms, or even in different specimens of the same 
species. Probably it often depends upon the circumstances under which the animal 
lives whether the embryonal shell is retained or not, and if it has been accidentally 
lost, whether its form be newly restored or not. 
I have no specimens of the true Dent. entalis, Linn., to compare, but Forbes 
and Hanley (Brit. Moll. II, p. 450) say that ‘the posterior termination has either a 
labial projection, which is rather broadly fissured dorsally (being ventrally), or, if 
it have not experienced that reparative process, is then very tapering, and has a 
short shelving notchlike dorsal (ventral) fissure.’ 
H. and A. Adams’ figure of <Antalis entalis exhibits the character of the 
ventral fissure very clearly. The opening in the supplementary tube is transverse, 
as usual in the Dawratup#; it is ventrally somewhat more prolonged, forming a 
kind of a notch and being in connection with the fissure of the shell. In. 
Dentalium the transverse opening of the supplementary tube, when present, is 
separate, not connected with the emargination of the shell. 
4. Fustiaria, Stoliczka, 1868. Shell tubular, thin, usually slightly curved, 
smooth, posterior end with a long, linear slit on or near the ventral side. 
Dentalinum eburneum, Lamck., Dent. circinatum, Sow., and others figured by 
Sowerby in his ‘“ Genera of shells,” by Deshayes in his last edition of the Paris 
fossils, etc., are typical species belonging to this generic group of the Dzyrazmpz. 
Comparing the shells of Fustiaria with those of Hntalis it will be seen that the 
former are usually smooth, thin, having the front part rather cylindrical and 
then quickly tapering towards the posterior end, the ventral side of which possesses 
a very narrow, linear slit; in Hntalis, on the contrary, the shell is usually more 
consistent and thicker, longitudinally striated, uniformly tapering from the anterior 
towards the posterior end, the slit being broad and short, specially widened at 
its termination. The relations and differences between these two genera are 
about the same which we have pointed out as existing between Pleuwrotomaria 
and Leptomaria (see p. 382). 
Some of the species, like the Dent. nebulosum, Desh., figured in Chenu’s Con- 
chological Illustrations, or our Fust. parvula from the Indian cretaceous deposits, 
