ACROLOXUS. 147 



ACROLOXLS, Beck. 



Tentacles and mantle as in Ancylus? Foot large. 



Shell dextral, elongated, oblong, patelliform, non-spiral; apex 

 near the middle, directed to the left ; aperture very wide ; peri- 

 treme continuous, simple, entire. 



Jaws (of A. lacustris) covered with crowded papillae ; upper 

 large, quite arched, laterals rather high, but little approached, 

 narrow, attenuated and pointed below. 



Lingual membrane with a central tooth, and twelve lateral 

 teeth on each side, then one tooMi of a dififerent form, and lastly 

 six more on each side. 



Acroloxus has a sinistral shell, the apex being on the left, but 

 the orifices of the animal are on the right. It further differs from 

 Ancylus in its lingual dentition. 



The name VeUeUia is sometimes used for this genus, because 

 Beck gave no description of Aa^oloxus. He gives, however, a 

 list of species sufficiently well known to make the generic distinc- 

 tion evident. 



I follow the same plan as in Atici/Ius in giving all the original 

 descriptions and figures of this genus. 



Acroloxus niittallii, Hald. — Shell fuscous, oval, elevated, apes 

 one-fourtli of the entire length from one end. Length J-3, breadth J, height 

 I inch. 



Oregon: Mr. Nuttall. (Haldeman.) 



Vellettia nuttaUii, Haldeman, Mon. pt. 3, p. 3 of cover (1841). — DeKay, 

 N. Y. Moll. 13 (1843). 



This is the only known recent species of North American 

 Acroloxus, unless Ancylus filosus, Conrad, should prove one. 



Ancylus filosus, Conrad. — Shell regularly oval, rather elevated, 

 with numerous radiating prominent lines ; apex very promi- 

 nent, inclined, eroded, not nearly central. -pia. 248. 



Inhabits the Black Warrior River, south of Blount's ^^^ 

 Springs, Alabama. It is abundant on various species of Sw^ 

 Melania. {Conrad.) ^S^ 



Ancylus Jilosus, Conrad, N. Fr. "W. S. p. 57 (1834) : ed. Ancylus 

 Chenu, p. 26.— Haldeman, Mon. p. 10, pi. i, f. 9 (1844). //osws. 



