100 PYRAMIDELLID^:. 



SHELL elongated : mouth slightly expanded, and having a 

 more or less complete peristome : pillar never furnished with 

 any fold or tooth. 



Perhaps this is an ill-assorted genus. More infor- 

 mation is desirable to clear up some doubts as to the 

 organization of its component species. 



Leach's genus Alvania, adopted by Searles Wood, 

 subsequently to Loven's publication, for Aclis suprani- 

 tida, comprised (according to Risso, who first described 

 that genus on Leach's authority) only certain species of 

 Rissoa. In Leach's own work the type of Alvania is 

 R. striata. 



(3\^t- 1. ACLIS U'NICA*, Montagu. N* 415 



Turbo unions, Mont. Test. Br. p. 299, t. 12. f. 2. A. unica, F. & H. iii. 

 p. 222, pi. xc. f. 4, 5. 



BODY clear- white, with very minute and close-set flaky 

 specks: mantle furnished with a cylindrical filament (as in 

 Hissoa) at the upper angle of the mouth of the shell : " muz- 

 zle slender and rather long, having the first half from the 

 neck, on its upper part, clothed with a very close tunic or tight 

 overlay; the disk is smooth, compressed, bevelled to a fine 

 edge, and almost circular, with a median vertical fissure on 

 the under surface, in which I have often seen the delicate 

 white corneous plates, jaws, and lingual riband : " tentacles 

 moderately long, flat, rounded or obtuse at the tips, quite 

 smooth even under high magnifying powers, and divergent : 

 eyes large and black, not on peduncles or prominences, but 

 fixed each on the centre of the base of either tentacle, with 

 very little external inclination, and widely apart ; on the march 

 the eyes are usually carried within the margin of the shell : 

 foot slender, greatly hollowed out in front, and deeply labiated, 

 having distinct, long, arched linear auricles which play or 

 vibrate when the animal is crawling, beneath [behind ?] which 

 it is slightly constricted ; it terminates in a rounded, rather 

 broad point ; no median line is apparent in any part of the 

 sole: opercular lobe simple. (Clark.) 



SHELL needle-shaped, thin, semitransparent, somewhat 

 * Unparalleled. 



