456 MR. §. PACE ON THE ANATOMY OF THE 
giliine *; but so very little has yet been published? respecting 
the internal anatomy of other allied forms, that it is not at present 
possible to assign any precise position within the subfamily to 
the two species dealt with in this paper. So far as our present 
knowledge goes, the nearest allies of these two forms, which are 
evidently representatives of distinct sections, would appear to be 
Pleurotomella, Verrill, and Spergo, Dall; and it is worthy of 
note that Dall describes Spergo glandiniformis, Dall, as possessing 
a rostral development which would seem to be not altogether 
unlike that of Pontiothauma. 
In the Toxoglossa generally the prestomial region is much 
specialized and often enormously developed ; and specialization 
would seem to reach its maximum expression in the truly 
remarkable rostrum of Pontiothawma mirabile. It is difficult, in 
the absence of any information as to the habits of the animal, to 
suggest an adequate explanation for the structural modification 
observable in this form. The appearance of the rostrum in P. 
mirabile is rather suggestive of a suctorial apparatus ; or, it may 
perhaps be that it is expressive of a habit of burrowing in the 
ooze and of enveloping its prey within the expanded rostral disk. 
Dall has suggested that the somewhat similar arrangement met 
with in Spergo is due to the habit of gorging itself with large 
masses of protoplasmic material, such as Foraminifera, rather 
than of attacking animals of a higher order. It should be stated 
that microscopical examination of the contents of the rhyncho- 
deum and of the alimentary canal has failed in either species to 
reveal any recognizab!e fragments of food-material: the contents 
consisted apparently merely of coagulated mucus. 
PoNTIOTHAUMA MIRABILE, L. A. Smith. (Pl. 42. figs. 1-9.) 
The single specimen, the type-specimen, upon which the fol- 
lowing notes are based was dredged in 1250 fathoms off the 
Malabar coast § by the ‘Investigator.’ It had been removed 
* Pontiothauma mirahile is by far the largest Pleurotomoid species at present 
known ; the shell of the type-speciinen has a length of 15°6 and a width of 
52 centimetres. 
+ Dr. Dall, who has had the unique opportunity of examining the compara- 
tively large number of deep-sea Pleurotomoids collected by the ‘ Albatross’ and 
other American expeditions, has unfortunately as yet published only a few ex- 
ceedingly slight and scrappy notes regarding their internal structure. 
+ Proc. U.S. Nat. Mus. vol. xvii. p. 681, pl. 24. fig. 1. 
§ Ind. Mar. Survey Station, No. 125. 
