RiSSOA. 



MOLLUSCA. 



79 



oval, oblique, pointed posteriorly, and anteriorly dilated, 

 generally with a slight sinus at the base of the columella; 

 lips nearly united, the outer one thickened, emarginated, 

 and not reflected ; operculum horny. 



1. E. ACUTA The Acute Rissoa, pi. XXXVIII. fig. 25, 



26. 



Rissoa acuta. Sowerby, Min. Conch. VI. p. 230, pi. 609, 

 fig. 2. 



Shell minute, elongated, turreted ; body somewhat shorter 

 than the spire, which consists of six moderately ventricose, 

 turreted, and gradually tapering volutions, terminating in an 

 acute apex ; aperture rather large, oblique, pointed both above 

 and below; outer hp considerably expanded; pillar lip a little 

 reflected on the columella; whole shell covered with longitudi- 

 nal, prominent ribs, numbering ten or twelve on each volution. 

 Length about three-sixteenths of an inch ; diameter not half its 

 length. 



Found in the Great Oolite at Ancliffe. 



2. R. L^vis The Smooth Rissoa, pi. XXXVIII. fig. 12. 



Rissoa lavis. Sowerby, Min. Conch. VI. p. 229, pi. 609, 



fig-1. 



Shell minute, oblong-oval, smooth, subcylindrical; body con- 

 siderably longer than the spire, which consists of five flat-sided 

 volutions, divided by a slight suture, and terminating in a 

 moderately pointed apex ; aperture placed obliquely, narrow, 

 slightly acute below, and rather sharp-pointed above ; outer lip 

 broad ; pillar lip a httle reflected on the base of the columella. 

 Length about an eighth of an inch ; diameter not half its 

 length. 



Found in the Great Oolite at Ancliffe. 



3. R. DUPLiCATA The Two-plaited Rissoa, pi. XXXVIII. 



fig. 14, 15. 



Rissoa duplicata. Sowerby, Min. Conch. VI. p. 230, pi. 

 609, fig. 4. 



Shell minute, elongated, turreted ; body occupying about 

 three-fifths of the shell ; spire consisting of five somewhat ven- 

 tricose volutions, with a flat spiral keel winding along their 

 centre, and terminating in a very sharp apex ; whole surface 

 covered with numerous longitudinal, straight ribs, which are 

 divided in the middle by the carina ; towards ihe base of the 

 body the ribs become obsolete ; aperture rather large, oblique, 

 oblong-oval, and pointed both above and below ; outer lip 

 broad ; pillar lip slightly reflected on the columella. Length 

 about an eighth of an inch ; diameter half its length. 



Found in the Great Oolite at Ancliff'e. 



4. R. OBLIQUATA The Oblique Rissoa, pi. XXXVIII. 



fig. 19, 20. 



Rissoa oUiquata. Sowerby, Min. Conch. VI. p. 230, pi. 

 609, fig. 3. 



Shell minute, elongated, subturreted ; body and spire about 

 equal in length ; the latter consisting of five moderately ven- 

 tncose and well defined volutions, terminating in a rather 

 blunted apex; whole shell invested by numerous oblique, curved 

 longitudinal ribs; aperture rather small, narrow, oblique, and 

 pomted both above and below ; outer lip broad ; inner lip nar- 

 rowly reflected on the columella. Length three-sixteenths of 

 an inch ; diameter somewhat more than a third of its length. 



Found in the Great Oohte at Ancliffe. 



5. R. puciLLA The Slender Rissoa, pi. XXXVII.* fig. 



22, 23, 24. 



Rissoa pitcilla. Brown, Trans. Manchester Geo. Soc. I. p. 



63, pi. 6, fig. 6, 7, 8. 



Shell smooth, ovate ; body large, inflated ; spire short, con- 

 sisting of three ventricose, deeply divided volutions, terminating 

 in a somewhat obtuse apex ; aperture ovate ; columella subum- 

 bilicate. 



This species differs from the R. Leighi in the volutions being 

 much less oblique, and being only one-sixteenth of an inch in 

 length, and nearly the same in diameter. 



Found in the Magnesian Marl at CoUyhnrst, near Manches- 

 ter, by E. W. Binney, Esq., and is in his cabinet. 



6. R. Leighi.— Leigh's Rissoa, pi. XXXVII.* fig. 25, 26, 

 27. 



Rissoa Leighi. Brown, Trans. Manchester Geo. Soc. I. p. 



64, pi. 6, fig. 9, 10, 11. 



Shell smooth, oblong-ovate ; spire long, consisting of four 

 deeply divided, inflated volutions, terminating in a somewhat 

 obtuse apex ; aperture ovate, slightly contracted above, and 

 rounded at the base ; columella subumbilicated. Length one- 

 eighth of an inch ; breadth one-fourteenth of an inch. 



Found in the Magnesian Marl at CoUyhurst, and is in Mr. 

 Binney's cabinet. 



7. R. MiNUTlssiMA. — The Very Minute Rissoa, pi. 

 XXXVII.* fig. 28, 29, 30. 



Rissoa minutissima. Brown, Trans. Manchester Geo. Soc. 

 L p. 64, ph 6, fig, 12, 13, 14. 



Shell smooth, slightly ovate ; body very large, ventricose ; 

 spire very short, consisting of two abruptly tapering, deeply 

 divided volutions, flattened above, and terminating in an acute 

 apex ; aperture nearly orbicular ; outer lip smooth, projecting 

 considerably from the body above. 



Found in the Magnesian Marl at CoUyhurst. In Mr. 

 Binney's cabinet. 



8. R. GiBSONi.— Gibson's Rissoa, pi. XXXVIL* fig. 31, 

 32, 33. 



Rissoa Gihsoni. Brown, Trans. Manchester Geo. Soc. I. p. 

 64, pL 6, fig. 15, 16, 17. 



Shell smooth, oblong-ovate ; spire and body of nearly equal 

 length; spire consisting of four not very oblique, but rapidly 

 decreasing volutions, terminating in an acute apex ; suture well 

 marked, but not deep; aperture ovate; outer lip smooth. 

 Length not quite a quarter of an inch; breadth somewhat more 

 than one-eighth of an inch. 



Found in the Magnesian Marl at CoUyhurst. In Mr. 

 Binney's cabinet. 



9. R. OBTUSA.— The Obtuse Rissoa, pi. XXXVIL* fig. 34, 

 35, 36. 



Rissoa obtusa. Brown, Trans. Manchester Geo. Soc. I. p. 

 64, pi. 6, fig. 19,20,21. 



Shell ovate, smooth, ventricose; spire nearly equal to the 

 body in length, consisting of three depressed, subturreted 

 volutions, divided by a deep suture ; aperture nearly orbicular ; 

 pillar lip not reflected, but provided with a slight umbilicus at 

 the base of the columella. Length upwards of a quarter of an 

 inch ; diameter not quite so much. 



Found in the Magnesian Marl, CoUyhurst. In Mr. Binney's 

 cabinet. 



