390 HETEROPHROSYNIDZ. 
pedicle, not formed by the fissure of any part of the head, 
divergent, very short, thick, very little flattened, of nearly 
the same size throughout, each pair connate with their re- 
spective stamens, very moderately setose, quite blunt at their 
terminations, beneath pale yellow, above delicately aspersed 
towards the extremities with pale-coloured very minute points. 
The eyes are large, black, placed very far back on the neck, 
on very slight eminences, perhaps immersed in them, appa- 
rently in a line with the centre of each tentacular pedicle. 
These parts were seen with great difficulty, and only came into 
view in two examples ; they however may be observed through 
the paler-coloured shells, but are not exserted on the march 
beyond the margin of the aperture. The foot is oval in 
quietude, showing a narrow lead-coloured margin, m action 
somewhat truncate anteriorly, with very small auricles, poste- 
riorly forming a gradually attenuated termination, without 
cirrhi, but slightly emargimate in one or two specimens. The 
testaceo-corneous operculum is suboval, marked with fine sub- 
annular striz, with a small central process, rib and groove, 
sometimes with two minute raised points or nuclei contiguous 
to each other ; all these characters are occasionally subject to 
some modification. We have several in our cabinet which 
differ materially, the annular strize of increment bemg usually 
permanent. The operculum is carried rather posteriorly, not 
on a developed operculigerous lobe. The foot is not labiated 
so as to produce a mentum—at least I saw none; it is 
not so slender proportionately as in the typical Rissoe, nor so 
long; beneath it is pale yellow, showing a medial line on the 
posterior half; above, elegantly mottled or brindled with dark 
close-set lead-coloured lines, which are sometimes waved ;— 
the colours on all parts vary in intensity in the different indi- 
viduals. I could detect no head-lappets. 
These animals float and creep like the Chemnitzie and 
Rissoe ; they inhabit the littoral and laminarian zones. 
Axis =},, diam. =}; uncie. 
The muzzle of this animal allies it to Rissoa, and the pecu- 
liar position of the eyes to Chemnitzia; further mvestigation 
is required to determine which is the most essential character. 
