HELICID^. 199 



are produced by a sudden contraction of the part 

 which forms a mould for the newly deposited portion 

 of the shell. 



12. VERTIGO Mutter. (Whorl Shell.) 



The animal, like Bnlimus, with only two elongate 

 clavate tentacles, the lower pair being wanting or 

 rudimentary, and with a subcylindrical, abruptly 

 obtuse shell, with close pressed, gradually enlarging 

 whorls ; the mouth contracted, more or less angular, 

 generally toothed internally, and thickened by an 

 exterior rib ; peristome simple. 



This genus has a shell very like the Pupce, but 

 was separated from them by Muller; and his division 

 has been adopted by most succeeding zoologists, be- 

 cause the animal has the upper pair only of tentacles, 

 which bear the eyes, developed. 



a. ISTHMIA Gray. (Ala?a Jeffreys.") 

 Shell dextral, cylindrical; mouth margined externally. 



69. 1. VERTIGO edentula. Toothless Whorl Shell, 

 (t. 7. f. 80.) Shell conic-oval, ventricose, brown, 

 with five or six volutions ; aperture semicircu- 

 lar, without any tooth ; the peristome simple, 

 without margin or rib ; umbilicus minute. 



Pupa edentula, Drap. p. 59. t. 3. f. 28, 29.; 

 Pfeiffer ; Alder, Mag. Zool. 8f Bot. ii. 112.; 

 Turton, Man. ed. 1. 99. t. 7. f. 80. 



Turbo Offtonensis. Sheppard, Linn. Trans, xiv. 

 155.? 



Vertigo nitida. Ferus. Tab. Moll. 64. 



Alsea nitida. Jeffreys, Linn. Trans, xvi. 358. 515, 

 K 4 



