100 PYRAMIDELLID^E. 



Shell elongated : mouth slightly expanded, and having a 

 more or less complete peristome : pillar never furnished with 

 anv 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. 



1. Aclis u'nica*, Montagu. 



Turbo unicus, 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 

 Rissoa) 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, fiat, 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. 



