TRTOCATELLA. 383 



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 mollusk, 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 extended, 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 

 margin and basally, straighter next the columellar side, and 

 contracted 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 me- 

 dially longitudinally 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 littori- 

 nidan vermicular character. 



That Truncatella is a Littorinidan genus admits of no doubt ; 

 the very paucispiral operculum, pair of jaws, and single bran- 

 chial plume sufficiently attest this determination ; its position 

 is of course closely connected with Rissoa. 



T. LITTOREA, Delle Chiaje. 



T. littorina, Philippi, Moll. Siciliae. 

 Rissoa et Assiminia littorea, nonnull. 



R. littorea, Brit. Moll. iii. p. 132, pi. 81. f. 6, 7; (animal) pi. M.M. 

 f. 3 a, 3 b, and iv. p. 265 (as Assiminia). 



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



