30 COLPODASPIS. 



The foot, upon this interpretation, must accordingly be described 

 as T-square shaped, with gracefully arched anterior wings and 

 rounded extremities, and of about the same length as the shell-bear- 

 ing portion of the mantle. The median furrow of its plantar surface 

 is shown in my drawing (fig. 2) to have the same extent as in Sars' 

 specimens. 



The Head. The grooved tentacles in my opinion correspond with 

 Sars' description, except that no mention is made in the latter of a 

 low curved ridge which can be seen in my figure 1 crossing the ante- 

 rior part of the head from side to side and connecting the postero- 

 dorsal edges of the two tentacles with one another. The eyes also 

 are much closer together in the Plymouth individual than they are 

 represented to be in Sars' figures; and the statement of the latter 

 that they are situated " close behind and within the base of the 

 tentacles" cannot be said to be applicable in the present case. I do 

 not, however, think that any great importance should be attached 

 to those slight discrepancies. 



When Colpodaspis pusilla is creeping upon a flat surface, the 

 antero-lateral horns of the foot are just perceptibly in advance of 

 the tentacles (fig. 1) ; but when the creature is swimming inverted 

 at the surface of the water the tentacles are then seen to be consider- 

 ably in front of the horns of the foot (fig. 2). 



The Body. I have no addition to make to Sars' account of the 

 body proper, except that in the Plymouth specimen the edges of the 

 pallial siphon were more closely opposed than seems to have been 

 the case with Sars' individuals. 



Pallial appendage. When the animal is creeping upon the bottom 

 of a vessel, a broad flattened tail-like appendage projects behind the 

 mantle and seems at first sight to be the posterior section of the 

 foot. Examination of the animal from the ventral aspect, how- 

 evers, reveals that this appendage is in reality a posterior prolonga- 

 tion of the hinder margin of the mantle to the morphological left of 

 the pallial siphon (fig. 2). 



In Philine catena also, according to Roule, the mantle terminates 

 posteriorly in a convex margin, a little below which are two fleshy 

 prolongations, "which can be mistaken for the posterior border of 

 the foot when the animal is contracted." His figures unfortunately 

 do not show this point at all well (pi. i, fig. 25), and Forbes and 

 Hanley's figure, though clearer, does not seem to represent the 

 anatomical relations correctly (1. c., pi. UU, fig. 4.) 



