6 Mr. W. Clark on the Genus Truncatella. 



ordinary extent beyond the aperture ; the head far exceeds the 

 tentacula m length ; these are short, flat, broad, subtriangular, 

 and diverge greatly, scarcely forming an angle of 25° ; the eyes 

 are large and black, and have white prominent pupils, which 

 visibly dilate and contract. I have never observed such in any 

 moUusk, though similar ones may have escaped notice ; they 

 are placed a little nearer to the base than the middle of their 

 lower half, not on pedicles, but quite flat on the centre of 

 subsemicircular expansions of the outer sides of the tentacula, 

 with an external tendency. Foot thick, steep, oval, very little ex- 

 tended, and on the march maintaining posteally and anteally the 

 oval contour, with a vermicular motion, like an advance of one 

 half to the other ; this action gives an apparent crease simulating 

 an incised transverse line, but on the step being completed the 

 foot becomes entire ; it carries very posteally on a plain upper 

 lobe, without an appendage of any sort, a narrow, irregularly 

 oval, light yellow corneous operculum, rounded at the outer mar- 

 gin and basally, straighter next the columellar side, and con- 

 tracted at the upper angle ; the nucleus of the spire is at the 

 base, with a single turn, which, though indistinct, is in certain 

 lights, with good glasses, quite visible ; its surface is coarse and 

 corrugated, and marked with rough, somewhat oblique, not 

 equidistant striae or ridges. The rostrum is medially longitu- 

 dinally finely grooved, which character extends through the 

 neck as far as can be seen, probably as a guide channel to the 

 branchial leaf. The neck, with this exception, is plain. The 

 animal is not shy, but does not creep with much rapidity ; its 

 progression is a modification of the littorinidan vermicular cha- 

 racter. That Truncatella is a littorinidan genus admits of no 

 doubt ; the very paucispiral operculum, pair of jaws, and single 

 branchial plume sufficiently attest this determination; its posi- 

 tion is of course closely connected with Rissoa. 



Truncatella littorea, Delia Chiaje. 



Truncatella littorina, Philippi, Moll. Sicilise. 

 Rissoa et Assiminia littorea, nonnuU. 



Animal inhabiting a minute pale yellow shell, not y^th of an 

 inch high, or in transverse measure, of four rather tumid volu- 

 tions, the first three of small areas, the body being more than 

 |ths of the bulk of the whole ; under powerful lenses in some 

 specimens the rudiments of the longitudinal costellse or striae of 

 Truncatella Montagui are visible, an important corroborative cha- 

 racter ; the peristome is complete, but sharp-edged. The animal 

 is of the jmlcst yellowish white, sprinkled with excessively mi- 

 nute flake-white points, particularly on the sole of the foot, with 



