SO 
ON THE ANATOMY OF PONTIOTHAUMA. 45% 
On the Anatomy of the Prosobranch Genus Pontiothauma, EB. A. 
Smith. By S. Pace. (Communicated by Professor G. B. 
Howes, LL.D., D.Se., F.R.S., Sec. Linn. Soc.) 
[Read 19th December, 1901.] 
(Prate 42.) 
Wuen, through the kindness of Mr. E. A. Smith, of the British 
Museum, an opportunity was, some few years ago, afforded me to 
examine the two deep-sea molluscs which form the subject of the 
present note, I gladly availed myself of it, since the members of 
that fauna occupying the deeper regions of the ocean almost 
invariably present the morphologist with features of particular 
interest. 
The molluscs in question formed part of the rich zoological 
booty which is being obtained by the Indian Marine Survey 
steamer ‘Investigator.’ Being submitted to Mr. Smith for 
identification, both species proved to be new to science; and, 
since they could not be relegated to any existing genus, Mr. Smith 
proposed * for their reception the new genus Pontiothauma, with 
type-species P. mirabile. The affinities of Pontiothauma, how- 
ever, appeared to be by no means clear; for, while the shell of 
the type-species presents a very close resemblance indeed to the 
whelks, the external characters of the animal seemed to be quite 
suit generis. Mr. Smith therefore asked me to examine the soft 
parts in order to determine the systematic position of the genus. 
This was done; but, since my investigations had only been based 
upon single specimens, which, being unique, one was naturally 
anxious to damage as little as possible, and further material 
being promised, I refrained from publishing at the time the 
details of my results. However, Pontiothauma does not appear 
to have been again met with; and it would therefore seem expe- * 
dient to place upon record the more important of such facts as 
could be made out from the original material. 
From the few characters which are recorded below, it will be 
evident that the affinities of Pontiothawma are with the Man- 
* Ann. & Mag. Nat. Hist. ser. 6, vol. xvi. p. 2. 
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