520 APPENDIX. 
Rissoa striata.—(P. 360.) 
Exmouth, July 1854. 
In our original notes it is stated that there is no cirrhus on 
the opercular lobe at its termination. Having reviewed a 
fine lively specimen, we found, beyond dispute, a short, white, 
pointed caudal filament. The pendent minute fillet at the 
upper and external angle of the aperture is present, though, 
as it is usually withdrawn, it cannot always be detected. 
The front of the foot forms a deep labium at the upper part 
by its separation from the sole; the flap is of the shape of 
the letter V inverted, the basal points bemg in front, and 
the angular one posterior; it is shadowed out by its flake- 
white composition, which is visible through the pellucid sole ; 
but the most smgular feature is, that its margins throughout 
are largely disunited from the upper part of the foot, bemg 
only fixed thereon by a central attachment. I have never 
before observed a similar labial structure, though it may 
exist in other animals and have escaped notice, for the foot in 
all the Gasteropoda is more or less labiated. 
Rissoa costata.—(P. 362.) 
Our notes are exact; mm a specimen examined in July 
1854, we cannot detect the filament we failed to find in 1852, 
at the upper angle of the aperture. Can it, instead of pro- 
ceeding from the mantle, as supposed by us, issue from the 
neck, and be the genitale of these minute creatures, which are 
considered bisexual? It is certainly much lower under the 
right tentaculum than is usual. If there is any weight in 
this conjecture, we must conclude that those species and 
specimens in which the filament is not visible are the females. 
What militates against these ideas is, that in some of the 
Rissoe we have found the organ in every example. This 
process is certainly not an edge of the operculigerous lobe 
that occasionally comes into view. 
Rissoa sotuta.—(P. 365.) 
The general colour is hyaline-white, suffused with very 
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