230 
RISSOA acuta. 
TAB. DCIX.- fig. 2. 
Spec. Char. Turreted, acute, costated ; costae 
many, longitudinal ; aperture large, outer lip 
much expanded ; whorls convex,, 7. 
A rather large aperture, a pointed, almost subulate 
spire, and ten or twelve rows of costae mark this species. 
RISSOA obliquata. 
TAB. DCI X.—fig. 3. 
Spec. Char. Elongated, pointed, costated; costae 
many, oblique, curved; aperture rather small; 
whorls 5 or 6, convex. 
Shorter in proportion to its width than the last, with 
fewer and oblique ribs and a smaller aperture ; other- 
wise much resembling it. 
RISSOA duplicata. 
TAB. DCI X.—fig. 4. 
Spec. Char. Elongated, pointed, costated ; costae 
very numerous, divided in their middle by a 
low carina ; aperture rather large. 
This beautiful little shell cannot fail to be easily recog- 
nized in all stages of its growth by the double set of ribs 
that extends from the central keel. 
These four species of almost minute shells are all from 
the Ancliffe Oolite. 
