390 HETEEOPHEOSYNID^:. 



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, in action 

 somewhat truncate anteriorly, with very small auricles, poste- 

 riorly forming a gradually attenuated termination, without 

 cirrhi, but slightly emarginate in one or two specimens. The 

 testaceo-corneous operculum is suboval, marked with fine sub- 

 annular striae, 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 striae of increment being usually 

 permanent. The operculum is carried rather posteriorly, not 

 on a developed operculigerous lobe. The foot is not labiated 

 so as to produce amentum at least I saw none; it is 

 not so slender proportionately as in the typical Rissoa, 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 Chemnitzia and 

 Rissoce ; they inhabit the littoral and laminarian zones. 



Axis -gL, diam. -^ uncise. 



The muzzle of this animal allies it to Rissoa, and the pecu- 

 liar position of the eyes to Chemnitzia ; further investigation 

 is required to determine which is the most essential character. 



