EMARGINULA. 258 



margin, and as many smaller intermediate ones ; sometimes these ribs 

 are equal in size ; they are crossed by from 20 to 30 somewhat 

 slighter concentric ribs, imparting a regularly and deeply can- 

 cellated or punctured appearance, and forming slight nodules at the 

 point of junction ; the surface is also covered with microscopical and 

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

 same white dots that have been been described with reference to 

 Puncturella noachina ; color white, often more or less stained by 

 extraneous matter ; beak very small, ribless, 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 direction, and usually exhibiting the 

 external larger ribs ; the sides of the slit are thickened, and the out- 

 side groove is represented by a white ridge. (Jejfr.') 



Length 9, breadth 7$, alt. 6 mill. 

 North-east Atlantic, from Finmark and Faroe Is. to the Canaries. 



Patella fissura~LiK*$. Syst. Nat. xii, p. 1261. E.fissura JEFFREYS 

 Brit. Conch, iii, p. 259, t. 59, f. 2. E. reticulata J. SOWEKBY, Min. 

 Conch., t. 33, lower figs. FORBES & HANLEY, Hist. Brit. Moll, ii, 

 p. 477. Sow. 2D. Thes., p. 214, f. 37, 38. #. cornea SARS, not 

 Schum. E. mulleri FORBES & HANLEY Hist. Brit. Moll., plates, t. 

 63, f. 1. E.lcevis, E.fissurata, E. tennis RECLUZ, Rev. Zool. 1843, 

 p. 232. E. emendata SOWB. Thes., p. 215, f. 11. Semperia paivana 

 CROSSE, Journ. de Conchy 1. 1867, p. 76, teste Watson. 



E. fissura is generally rather straightly conical, the apex not 

 much behind the middle and never extending over the hind margin 

 of the shell. It is more elevated than any of the preceding species. 



Var. 1. subdepressa. Somewhat larger, more depressed, and ex- 

 panded at the sides. (Jejfr.) 



Var. 2. elata. Also larger than usual, much higher, and more 

 solid. (Je/r.-) 



Var. 3. incurva. Smaller, more raised, and compressed at the 

 sides, with the beak almost overhanging the posterior margin ; 

 sometimes of a pinkish color inside. (Jeffr.) 



The edges of the fissure are sometimes in contact at the edge, giv- 

 ing rise to the form described by Sowerby as E. emendata (pi. 28, 

 fig. 14), and by Crosse as Semperia paivana. 



