33 



the relationshiij of which either to the sponges or to the Khizo])odes, we have not 3'et arrived 

 at any clear notion. The posterior end of the shell is extremely thin, and usually almost 

 perfectly straight; as in our two other species of Dentalium. the apex is obliquely truncated 

 (fig. 8) the posterior opening of the shell below forming a tolerably deep incision (see fig 7). 

 Inside this opening one often sees the supplementary tube, which terminates in the same 

 manner, but only projects a little beyond the extremity of the original shell. 



Sometimes — although apparently more rarely — the shell exhibits a more or less 

 distinct longitudinal striation (see fig. 5); but this striation is always only slightly marked, and 

 never forms such salient longitudinal ribs as in the D. abyssorum; moreover it is always 

 confined to the posterior part of the shell. 



In the smallest of the specimens found by me, the embryonic shell remained (fig. 14). 

 It is nearly straight, smooth and tolerably lustrous, also finely cross-ringed, whereby the out- 

 lines, especially towards the posterior part, appear finely creniilated. The apex is (see fig. 

 15) somewhat enlarged, and evenly convex, without stripes or rings, and terminates with 2 

 small collateral points, between which the small circular aperture is situated. 



The Animal is of the usual form for this genus. The foot (see fig. 10 & 11) is, when 

 fully extended, about ^|^ the length of the shell, slender, cylindrical and at the extremity as 

 usual three-lobed. The middle lobe, which represents the proper extremity of the foot, is 

 conically pointed, terminating in a fine point, and considerably longer than the side lobes. 

 The latter are thin, membranous, closely folded longitudinally, and nearly surround the basis 

 of the middle lobe like a frill. In front of the protrusible part of the mantle, which reaches 

 beyond the aperture of the shell, there are to be observed numerous so-called captacula, 

 curved and bent in all directions, with which the animal brings food to its mouth. The pos- 

 terior spoon-shaped appendage to the body (fig. 12 & 13) is considerably longer and nar- 

 rower than in the D. Abyssorum, somewhat inequilateral, and has on the ventral side a long 

 and narrow incision. 



The animal is remarkably active in its movements, much more so than I have found 



to be the case with our 2 other species of Dentalium: and it is also precisely this which 



has given rise to the specific name. The manner in which it uses its foot, partly to bury 



itself in the mud, partly for locomotion in one direction or in another is really so energetical, 



that one would at first glance be inclined to believe the animal a Siphonodentalium rather 



than a Dentalium. As is the case with the former, a considerable time may pass, before one 



can see these movements; for the animal will frequently remain obstinately retracted in its 



shell, during which time however the anterior part of the mantle togethei", with a greater or 



smaller number of the filiform captacula, will usually be seen i)rojecting beyond the aperture 



of the shell. By these latter, which certainly do not only serve as instruments of capture, 



but also act as real feeling organs, the animal appears, as it were, to survey the ground before 



extending its foot. This operation takes place very rapidly, just as with the Siphonodentalium, 



the foot being advanced suddenly beyond the aperture of the shell, with the side lobes lying 



5 



