some nexo and peculiar Mollusca. 237 



I notice tliis and a fow otlior species wliich are common in 

 tlie arctic seas, because 1 am able to give a description of the 

 animal. 



Trochus umhilicah's, Broderip and Sowerby. 

 Marqarita iitiibi/icah's, Brod. & Sow. in Zool. Jouni. vol. iv. 1829, 



p. "an. 



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

 ^/idc Hancock). Wellington Channel (Belcher). Lancaster 

 Sound (Sir J. C. Ross). Loom Bay, Spitzbergen (P^aton) ! 

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

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

 Kane Valley, N. lat. 82° 88' (Feilden) ! 



Body yellowish : head horseshoe-shaped and prominent ; 

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

 cilia : ei/es 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) filaments at the end or 

 tail of the foot. The animal diflfers from that of T. Groen- 

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

 slender tentacles, and in T, Granlandicus being destitute of 

 caudal filaments. 



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

 believe they are distinct species. I have specimens of each 

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

 2\ umhilicah's 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. umbilicalis of Da Costa, which is T. umhilicatus of 

 JMontagu, and T. ninhilicaris of Pennant, but not of Linn^. 

 Such a ringing of the changes is inconvenient. 



Trochus olivaceuSj Brown. 



Turbo olivaceus, Brown, lUustr. Brit. Conch. 1827, pi. 4G. f. 30, 31 

 (no pajre). 



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 : cj/es placed on small bulbs at 

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

 double-edged in front, bUnUly ])ointed behind ; appendages 3 

 on each side on the u])i)cr ])art of the foot, shortish, finely 

 cjliated like the tentacles. Animal active. 



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

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



