336 TROCHIDJE. 



we should call stifling or suffocating. Another peculiar 

 habit of such mollusks is worthy of notice, and is one 

 which I cannot pretend to explain. It is the faculty of 

 floating. Now it is very certain that in their native 

 habitat, at a depth of from 150 to 540 feet, these shell- 

 fish, being ground-dwellers and having no organ or 

 means by which they can rise to the surface, could never 

 exercise this faculty. Is it instinct that teaches them to 

 float after ha^dng been forcibly dragged from the bottom 

 of the sea and put into a shallow vessel of water ? and if 

 so, when was it implanted? Two living specimens, 

 which I took in the same spot, differed in the colour of 

 the animal, although the shells were undistinguishable. 

 One was of a uniform yellowish-white, while the other 

 was milk-white and had the sides of the foot streaked 

 \vith brown. Mr. Alder says that the tongue is very 

 beautiful and of a complicated structure, and that the 

 uncini on each side are extremely numerous. It agrees 

 in general character with that of T. zizyphinus : indeed 

 the animals of both are much alike. The first whorl of 

 the fry is exquisitely reticulated, like Lagena squamosa. 

 The present species is the T, alabastruni of Beck (ac- 

 cording to Loven), T. quadricinctus of S. Wood, and 

 Ziziphinus alabastrites of Gray. No wonder that 

 Forbes, who described this shell as a new species, gave 

 it the name of formosus. It is truly beautiful ; and we 

 offer but faint praise in saying of such splendid prizes 

 of the dredger — 



" There's not a gem, 



Wrought by man's hand to be compared to them." 



