030 PLIOCENE MOLLUSCA. 



Scacclii. While, however, there has been considerable difference of opinion as to 

 its relation to II. Gueriid, there can be little doubt, I think, that it agrees with 

 Alder's R. costukda. I venture, however, to retain the former name for our shells, 

 if only provisionally. 



The Rissoa costidata of the first part of Wood's Monograph of 184-8 (p. 106, 

 pi. xi, fig. 12) is evidently a different species, B. Sfefanisi (Jeffreys), Menestho 

 Stefanisi (nobis), as indeed he pointed out in his 1st Suppl., p. 73, 1872. 



Rissoa dissimilis, sp. nov. Plate LI, figs. 5, G. 



1898. Rissoa obscura, A. Bell, Traus. Roy. Geol. Soc. Cornwall, vol. xii, p. 153. 



Specific Characters. — Shell minute, elongato-conical, obtusely angulate at the 

 periphery; whorls 6 or 7, nearly flat; ornamented by about 12 longitudinal ribs, 

 strong, rounded and prominent on the last, less so on the u])per ones, ending at 

 the angulated base, and by fine spiral ridges which are more strongly marked 

 below the angulation ; spire regularly diminishing in size to a blunt point ; suture 

 well marked, l)ut not deep; mouth ovate, angulate above. 



Dimensions. — L. 3 mm. B. 2 mm. 



Disfribiifion. — Not known living. 

 Fossil; St. Erth. 



Bemarks. — The specimens from the British and Caml)ridgo Museums figured 

 nnder this name, both obtained at St. Erth, were at first identified by Mr. Bell 

 with the B. obscura of Philippi, but they are now considered })oth by him and by 

 myself as belonging to a different species. As to the latter, he remarks that in 

 his shell the whorls are " valde convexis," and they are shown to be so in his 

 illustration, whereas in our fossil they are nearly flat. The one from the British 

 Museum (no. 18106) is there named 7?. radiata, but I doubt whether this is correct. 

 It seems to me that they are both the same, and I prefer to regard them as new. 



Rissoa parva (Da Costa). Plate LI, figs. 11, 12. 



1779. Turbo parvus. Da Costa, Brit. Conch., p. 104. 



1801. Turbo lacteus, Donovan, Nat. Hist. Brit. Shells, vol. iii, pi. xc. 



1853. Rissoa imrva, Forbes and Hanlev, Brit. Moll, vol. iii, p. 100, pi. Ixxvi, fig. 6. 



1859. Rissoa imrvai G. B. Sowerby, 111. lud. Brit. Shells, pl. xiii, fig. 16. 



1867—84. Rissoa parva, Jeffreys, Brit. Condi., vol. iv, p. 24, 1867 ; vol. v, p. 207, pl. Ixvii, fig. 3, 



1869 ; Quart. Journ. Geol. Soc, vol. xl, p. 319; Proc. Zool. Soc. London, p. 118, 1884. 

 1870—98. Rissoa parva, A. Bell, Journ. de Conch., vol. xviii. p. 351, uo. 390, 1870 ; Proc. Roy. Phys. 



Soc. Edinb., vol. x, pp. 292, 296, 1890; Proc. Yorks. Phil. Soc, p. 63, 1892 ; Proc. Roy. Irish Acad. 



[3], vol. li, p. 629, 1893; Trans. Roy. Geol. Soc. Coinwall, vol. xii, p. 153, 1898. 

 1874 — 76. Rissoa parva, Seguenza, Boll. R. Com. Geol. Ital., vol. v, p. 4, no. 359, 1874 ; vol. vii, 



p. 102, no. 680, 1876. 



