OF SOUTHERN INDIA. 437 
and again that the eyes become rudimentary or disappear altogether as soon as the 
necessity for their use ceases, like in many of the species of the OprsrHo- and 
PROSO-BRANCHIA which bore in sand. Thus similar imperfections in the organisa- 
tion as they occur in the ProsopocrPHata are actually common in other orders of 
the Gastropoda, and the same may be said with regard to the symmetrical develop- 
ment of some of the organs. 
Sub-order,—Scaphopoda. 
Family,—DENTALITD 4. 
For the present only the Deyrazrrp can be referred to the sub-order Scarno- 
Popa, the animals being characterized by a muscular foot, adapted for digging ; 
at its termination, it being either provided with very short lappets or axgaanadlenl Hat 
a kind of a disk. These differences in the form of the foot are accompanied by 
others relating to the organs of secretion and generation. 
There are at the present only very few genera of the Deyrazizpz sufficiently 
established, but I think that even according to our present, as yet imperfect, 
knowledge of the animals and shells, they can conveniently be separated into two 
sub-families, aw74zin# and GADILINZ. 
a, Sub-family,—ANTALINZ. 
The animals possess a short, thick, anteriorly grooved foot, being either simply 
pointed at its termination or provided with short lappets; liver symmetrical, consist- 
ing of two equal parts. 
Shell rather solid, elongated, tapering towards the posterior, pointed and per- 
forated end, with or without a slit on the ventral* side. 
1. Dentaliwm, Aldrovandus, 1642 (De testaceis, Lib. III, cap. V, p. 282—id., 
Linné et auctores, H. and A. Adams, Gen. I, p. 456). Animal with a short foot, 
anteriorly thickened and tripartite. Shell tube-like, gradually tapering posteriorly, 
longitudinally ribbed, margin of the aperture sharpened, posterior end with an 
internal, slightly projecting tube, which is provided with a dorso-ventrally elongated 
opening, the outer layer having a very slight emargination in the same diametral 
direction, namely, dorso-ventrally. 
Having examined a number of well preserved recent species, I believe the 
name Dentalium ought to be reserved for these longitudinally ribbed forms, as 
first pointed out by Aldrovandus. The shell has posteriorly no fissure, but the 
posterior margin of the outer layer is slightly indented on the dorsal as well 
as on the ventral side. The Indian Dentalium sulcatum of daCosta and Lamarck, 
or Dent. elephantinum, Linn., may be considered as the types of this genus. There 
are a number of recent and fossil species of this and the next genus known, which 
* According to the anatomical results obtained by Sars, the concave side is the dorsal and the convex the 
ventral. 
5P 
