230 A MANUAL OF AMERICAN LAND SHELLS. 



it may be that these are annual. The growth seems to go on actively 

 for a time, by the addition of new testaceous matter, indicated by the 

 oblique striae, and then alternates with a season of repose, when the 

 teeth and aperture are formed. The teeth appear never to be entirely 

 absorbed and removed, although the aperture, near which they were 

 originally i:>laced, is often advanced very far beyond them. When in 

 motion the shell lies horizontally on the animal's back. 



A curious subject of investigation is the albinism, or entire absence 

 of coloring matter, in the shells of certain individuals of this and other 

 species. The albinos of this sjjecies are of a i)ure, lively white, while the 

 contained animal is highly colored. Mr. Anthony remarks that about 

 one-seventh of all the specimens collected by him in the neighborhood 

 of Cincinnati are colorless. As they are apparently operated upon by 

 the same physical agents which influence the others, it is not easy to 

 conjecture how this singular effect is produced. The animal is some- 

 times cream-colored throughout; but in such instances the shell is 

 usually colored. 



Animal with head, neck, and eye-peduncles bluish-black or slate-color; 

 margin and posterior part of foot white. Eye-peduncles very long, 

 tentacles very short; body narrow and delicate, in length not much 

 exceeding the diameter of the shell. I cannot detect any caudal mucus 

 pore, but it is difficult to see any such, even if existing (as I believe it 

 must), on account of the extreme transparency of the animal. 



Jaw slightly arcuate, ends attenuated, pointed; a median, beak-like 

 projection to the cutting edge. 



Lingual membrane as usual in Zonites (Terr. Moll., V, Plate III, Fig. 

 Q), with 28-1-28 teeth; 4 laterals. 



The genital system has the dart sac and dart of ligerus, 



DOUBTFUL SPECIES OF ZONITES. 



Zonites cultellaius (see Terr. Moll., iv, 22, pi. Ixxvi, fig. 6). This species must be 



removed from our catalogue, not having again been found in, and most 



probably not belonging to, our limits. 

 Zonites Netcberryana (I.e. iv, 20) is a species of the Helicea, now described as anew 



genus, Ghjptostoma, q, v. 

 Zonites alUarius has been foi;nd in hot-houses in Brooklyn, N. Y., and Chicago. It is 



said by Morch to be found in Greenland (Amer. .Tourn. Conch., iv, 29). 

 Zonites Lansingi. See Microphysa. 



FOSSIL SPECIES OP ZONITES. 



Zonites (Conuliis) prisons, Carpenter, Quart. Journ. Geol. Soc, 1867, 331, with figs. 



Nova Scotia. 

 Helix {Zonites) marginicola, Conrad, Am. Journ. Couch., vi, 315, pi. xiii, fig. 9 (1871). 



Oregon. 



