some new and peculiar Mollusca. 237 



I notice this and a few other species which are common in 

 the arctic seas, because I am able to give a description of the 

 animal. 



Trochus umbilicalis^ Broderip and Sowerby. 



Margarita umhilicalis, Brod. & Sow. in Zool. Journ. vol. iv. 1829, 

 p. 371. 



Station 4j 20 fms. Davis Strait (Warham and Harrison, 

 Jide Hancock). Wellington Channel (Belcher). Lancaster 

 Somid (Sir J. C. Ross). Loom Bay, Spitzbergen (Eaton) ! 

 Arctic Expedition, 1875, F. Pierce Baj, N. lat. 79° 25', 

 15 fms. ; Discovery Bay, N. lat. 81° 41', 5\ fms. ! Fossil in 

 Kane Valley, N. lat. 82° 33' (Feilden) ! 



Body yellowish : head horseshoe-shaped and prominent ; 

 tentacles thread-shaped, covered with very fine and close-set 

 cilia : eyes on small bulbs at the outer base of the tentacles : 

 foot long and slender ; pedal filaments numerous, ciliated like 

 the tentacles, each filament provided with an ocellus or eye- 

 spot at its outer base ; there are six on each side, and several 

 other smaller (some of them double) fidaments at the end or 

 tail of the foot. The animal differs from that of T. Ora>n- 

 landicus (which is found with it) in having shorter and less 

 slender tentacles, and in T. Groenlandicus being destitute of 

 caudal filaments. 



It is Moller's variety Icevior of T. Groenlandicus ; but I 

 believe they are distinct species. I have specimens of each 

 from Spitzbergen agreeing in size and the height of the spire. 

 T. umhilicalis has a more expanded shape and thinner texture; 

 and the umbilicus is always more open and wide. The sculp- 

 ture varies in both. 



Not T. umhilicalis of Da Costa, which is T. umhilicatus of 

 Montagu, and T. umhilicaris of Pennant, but not of Linn^. 

 Such a ringing of the changes is inconvenient. 



Trochus olivaceus, Brown. 



Turbo olivaceus, Brown, lUustr. Brit. Conch. 1827, pi. 46. f. 30, 31 

 (no page). 



Body milk-white : head semicircular, finely and regularly 

 notched in front, and having on each side a small triangular 

 lappet : tentacles thread-shaped and slender, covered with 

 close-set and microscopic cilia : eyes placed on small bulbs at 

 the outer base of the tentacles : foot broad, rounded and 

 double-edged in front, bluntly pointed behind ; appendages 3 

 on each side on the upper part of the foot, shortish, finely 

 ciliated like the tentacles. Animal active. 



Station 3, 100 fms. ; 4, 20 fms. ; 5, 57 fms. ; Holsteinborg, 

 10 fms. Greenland (Moller) ! United States, north of Cape 



