RISSOA MH:MHIIANA(:EA. 625 



Pleistocene : Monte Pellegriiio, I'.iranto, Ijivorno, Valle Biaia, sub-Btnaen 

 beds — Nizzeti. Rliodes. 



Renuirha. — IMiis little shell, easily recognisable, is as a fossil known from Selsey, 

 Bridlington, Glop[)a and several other Bi'itish localities ; it seems, however, to be for 

 the most part a sonthern form. It is grouped by the Conchological Society with 

 It. zetlandica as generically distinct. 



Genti.^ RISSOA Fremenville, 1813. 

 Rissoa membranacea (A. Adams). Plate LI, fig. 1. 



1797. Turbo menibranaceus, A. Adams, Tnius. Liim. Soc, vol. v, p. 2, pi. i, figs. 12, 13. 



1846. Rissoa membranacea, Lov('u, K. Svensk. Vet.-Acad. Forli., vol. iii, p. 96. 



1867 — 69. Bissoa meiiibyanacea, JeEveys, Bv'it. Condi., vol. iv, p. 30,1867; vol. v, p. 208, pi. Ixvii, 



fig. 8, 1869. 

 1873. Rissoa inembranacea, Weinkauit', Cat. europ. Meeresconcli., p. 18, no. 278. 

 1878. Rissosfomia membranacea, G. 0. Sars, Moll. Reg. Arct. Norv., p. 359. 

 1878 — 84. Rissoa membraHacea, Monterosato, Euum. e Sin. Conch. Medit. (Giorn. Soc. Sci. Nat. 



Palermo, vol. xiii, p. 83), 1878; Zippora fray His, Nom. Gen. e Spec. Conch. Medit., p. 54, 1884. 

 1892. Rissoa membranacea, Praeger, Proc. Roy. Irish Acad. [3], vol. ii, p. 260. 

 1892—98. Rissoa membranacea (pt.), A. Bell, Rep. Yorks. Pliil. Soc, p. 63, 1892 ; Proc. Roy. Irish 



Acad. [3], vol. ii, p. 630, 1893 ; Trans. Roy. Geol. Soc. Cornwall, vol. xii, p. 153, 1898. 

 1901. Zippora membranacea. Conch. Soc. List, Jovirn. of Conch., vol. x, p. 18, no. 326. 

 1913. Rissoa membranacea, Dautzenberg et Durouchoux, Feuille des Jetines Natur., vol. xliv, p. 28. 



Specific Characters.- — Shell rather thin, semitransparent, oblongo-conical ; whorls 

 7, somewhat compressed, the last much the largest, expanded below, half to two- 

 thirds the total length ; ornamented on the three lower whorls by prominent, 

 somewhat flexuoiis ribs, which do not reach the base, the upper ones being 

 without such sculpture, the labial rib being thick and broad, also by exceedingly 

 delicate spiral lines; spire elongated, with a sharp point; mouth oval, expanded; 

 inner lip reflected on the pillar and on the base. 



Dime)i>>ioii!y. — L. 8 mm. B. 4 mm. 



Dii^fribiifioii. — Recent .- British coasts from low-tide mark to a few fathoms, 

 local ; Atlantic from Noi'way and Denmark to France, Spain and the Canaries. 

 Mediterranean, vEgean, Adriatic. 

 Fossil: St. Erth. 



Pleistocene : Selsey, Bute, Clyde beds. Largo, Kelsey Hill, Bstuarine clays of 

 Belfast. Uddevalla, Norwegian coast. 



Remarks. — ^This common British species has not been reported from the 

 English Crag, though there is a rather unsatisfactory specimen in the British 

 Museum from St. Erth which has been identified with it. Those of the type 

 and its varieties now figured are from the estuarine beds of Belfast, where it is said 



