260 FISSURELLID^E. 



imparting a regularly and deeply cancellated or punctured 

 appearance, and forming slight nodules at the points of junc- 

 tion ; the surface is also covered with microscopical and 

 close-set longitudinal striae, and in the young may be ob- 

 served the same white dots that have been described with 

 reference to Pitncturella Noacliina : colour white, often more 

 or less stained by extraneous matter : beak very small, rib- 

 less, incurved and slightly twisted to the left, forming a 

 spire of two whorls : slit of equal width, extending from the 

 margin in front about one-third of the way up, where it is 

 closed by a subsequent formation of shell, and becomes as 

 far as the crown a rather deep groove, which is somewhat 

 closely laminated across : mouth roundish-oval, distinctly 

 scalloped and notched by the indentation of the longitudinal 

 ribs : inside nacreous, finely lineated in a concentric direc- 

 tion, and usually exhibiting the external larger ribs : the 

 sides of the slit are thickened, and the outside groove is 

 represented by a white ridge. L. 0-45. B. 0-35. 



Var. 1. subdepressa. Somewhat larger, more depressed, 

 and expanded at the sides. 



Var. 2. data. Also larger than usual, much higher, and 

 more solid. 



Yar. 3. incurva. Smaller, more raised, and compressed at 

 the sides, with the beak almost overhanging the posterior 

 margin ; sometimes of a pinkish colour inside. 



Habitat : Everywhere on shells and stones, from 

 low-water mark at spring tides to 90 f. ; off the Mull of 

 Galloway, in 110-145 f. (Beechey) . Var. 1. Shetland, in 

 deep water. Var. 2. Fishguard, and Larne near Belfast 

 (J. G. J.). This variety also occurs in the Red Crag; 

 it is nearly as high as long. Var. 3. Oban, Skye, and 

 Shetland (Barlee and J. G. J.). E.fissura is fossil in 

 Ireland, according to Mr. James Smith ; and it is rather 

 common in the Red and Coralline Crag ; Antwerp ter- 

 tiaries (Nyst) ; Christiania, in the newer glacial forma- 

 tion, 150-200 ft. (Sars) . Living in the North Atlantic, 

 from Finmark and the Faroe Isles to the Canaries (where 



