OF SOUTHERN INDIA. a7; 
simple ovate foot of Struthiolaria is elongated, laterally compressed in Aporrhais, 
partially divided in Terebellum, and entirely divided into two separate lobes in 
Lostellaria, &e. 'The same might be said as regards the eyes; the small bulgings at 
the base of the tentacles of Struthiolaria are replaced by short pedicles in Aporrhais; 
these pedicles are prolonged (and probably united with the tentacles throughout their 
entire length) in Terebellwn; while in Rostellaria, and others, they are usually sepa- 
vated from the tentacles near the termination, where the eyes are placed on the former. 
It is true, that other Gastropoda shew similar relation in the same points, and 
still are regarded as belonging to different families; but it must be remembered, 
that they do not agree in all the other similarly or more important characters, which we 
have previously noticed. ‘Taking all these facts into consideration, it must be granted, 
that the structure of the animals does not lend itself very favorably to such a separa- 
tion into two families as has been proposed by Adams, Gray and others. There would 
be far less difficulty experienced in this matter by accepting Adams’ proposition of 
the two sub-families of srtrousrnz and TEREBELLINZ, and by adding to these his 
family Arorra4arDz as a sub-family arorrHary#, although I actually do not know, 
whether even this separation is necessarily called for. Supposing, however, that it were 
so, the distinctions between these sub-families would be those which I have specified 
regarding the foot and the eye-pedicles, while the other points of relation, quoted 
above, would form the character of the family. 
These questions could all be easily settled, had we to deal with the living species 
only, but what is to be done with the immense number and great variety of fossil 
forms? To determine these with equal correctness, we ought to have distinctions in 
the form of the shell, equally characteristic with those we have noticed in the animals 
themselves. And if, as is often the case, we cannot determine with sufficient accu- 
racy the genus, how difficult it must be to retain sub-families! Chenu consequently 
recognized only one family, the S'rromerpx, containing seven genera and a few 
sub-genera. In ageneral view this appears to be, provisionally, the best way : but the 
number of genera in living and fossil species must be enlarged, and those so-called 
sub-genera as much as possible avoided. At the same time, it cannot be questioned, 
that our object ought to be to endeavour to prove the existence of similarities and 
differences of the shells, in accordance with the results obtained from a careful 
examination of the animals, rather than to obliterate or ignore these on the suppo- 
sition that they never existed before. It may be a very plausible conjecture, that 
these distinctions did not exist at some remote period, as some of our most able 
palzontologists are ready to believe, but we must first point out, at least approxi- 
mately, what that period was. Nor can we ever establish this, until we carefully 
and gradually trace back these relations from the recent into the older formations. 
We shall recur to this point when speaking of Alaria and Aporrhais. 
In treating of the different genera of the Azra, it will not be necessary to go 
beyond what is justified by the material we have before us in describing our 
eretaceous fossils. To discuss these points fully would require a thorough know- 
ledge of all the species both living and fossil. It is undoubted, that there are great 
difficulties in determining the distinctions of the sub-genera as proposed by H. and 
F 
