RrssoA. 
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. R. 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 lip 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. LiEVis.— 1 The Smooth Rissoa, pi. XXXVIII. fig. 12. 
Rissoa Icevis. 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 little 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 the 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 Ancliffe. 
4. R. obliquata. —The Oblique Rissoa, pi. XXXVIII. 
fig. 19, 20. 
Rissoa obliquata. 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¬ 
tricose 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 
pointed 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 Oolite at Ancliffe. 
5. R. pucilla. —The Sleuder Rissoa, pi. XXXVII.* fig. 
22, 23, 24. 
Rissoa pucilla. 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 Collyhnrst, near Manches¬ 
ter, by E. W. Binney, Esq., and is in his cabinet. 
6. R. Leigiii. —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 Collyhurst, and is in Mr. 
Binney’s cabinet. 
7 . R. minutissima -The Very Minute Rissoa, pi. 
XXXVII* fig. 28, 29, 30. 
Rissoa minutissima. Brown, Trans. Manchester Geo. Soc. 
I. p. 64, pi. 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 Collyhurst. In Mr. 
Binney’s cabinet. 
8. R. Gibsoni. —Gibson’s Rissoa, pi. XXXVII.* fig. 31, 
32, 33. 
Rissoa Gibsoni. Brown, Trans. Manchester Geo. Soc. I. p. 
64, pi. 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 Collyhurst. In Mr. 
Binney’s cabinet. 
9. R. obtusa. —The Obtuse Rissoa, pi. XXXVII.* 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, Collyhurst. In Mr. Binney’s 
cabinet. 
