RISSOA. 25 



Var. 2. exilis. Dwarf, very slender, thin and smooth, tawny, 

 without any conspicuous markings ; labial rib wanting or ru- 



dimentary. By *o rne^S rcre '* Tfc *, tff 



HABITAT : Swarming on seaweeds and Zostera at low- 

 mark and throughout the laminarian zone. Ac- 

 cording to Alder a variety has been taken among coral- 

 lines from 20 f. The typical form is more common in 

 the south, and the variety interrupta in the north ; both 

 live together, as well as every conceivable gradation as 

 regards shape, size, solidity, sculpture, and colour. 

 Some are full-ribbed, some half-ribbed, and some have 

 only the traces of ribs on one or other of the larger 

 whorls; but the top whorls are invariably smooth. 

 The 2nd variety was found by me in Lerwick Sound. 

 Sars has recorded the typical form as fossil in the post- 

 glacial beds of Norway, at heights between 40 and 

 200 feet; and the variety interrupta has occurred in 

 upper tertiary deposits in Ireland (Brown) , Fort William 

 (J. G. J.), Dalmuir and Clyde beds (Crosskey and 

 others), Uddevalla (J. G. J.), Christiania district, in 

 the newer or post-glacial strata, at 100 feet (Sars), 

 Nice (Risso) . The foreign distribution of this species 

 and its principal variety comprises the coasts of Upper 

 and Lower Norway, Sweden, Denmark, Holland, France, 

 Spain, Portugal, Italy, Dalmatia, Greece, Algeria, and 

 the Canary Isles, from the shore to 40 f. In the ' Zoolo- 

 gical Record ' for 1864, von Martens questions the R. ob- 

 scura of Philippi (which is the typical form of this species) 

 being Mediterranean, because he had not found it there. 

 It is not uncommon at Spezzia. 



. Lying on a rock by the brink of a seaweed- covered 

 pool left by the receding tide, it is no less pleasant than 

 curious to watch this active little creature go through its 

 different exercises creeping, floating, and spinning. 



VOL. iv. c 



