North American Terrestrial IfoUusks. 165 



received from Miss Law, of H. interna; it may, however, 

 have escaped our notice, being often difficult of detection. 



The orifice of a^eneration in the s^enns Zonites is said to be 

 at the base of that of respiration, below the collar, and not 

 below the right eye-peduncle as in Helix. It may be much 

 doubted, however, whether this be a constant generic charac- 

 ter, as it is found in some species of the former much nearer 

 to the head than the collar. 



The dart sac and dart were observed by us in specimens 

 of Zonites clemissus and Z. ElUotti. They have also been 

 noticed by Morch (Moll. Dan. ) in Zonites ( Oxychilus) nitidus. 

 The description of Albers and v. Martens must therefore be 

 modified, as well as Moquin Tandon's assertion that no 

 species of Zonites has the dart.* 



Subfamily Helicin^. — The following description is to be 

 substituted for that given at p. 67. 



Jaw in one piece, either smooth, striated, or ribbed, with 

 or without a median beak-like projection to its cutting edge. 

 Lingual membrane with crowded, quadrate marginal teeth, 

 either dentate or serrate. 



The ribs are found in every degree of development, pass- 

 ing quite across the jaw and denticulating one or both 

 margins, or only developed on the lower portion of the jaw, 

 and crenellating the lower margin. The ribs are often al- 

 most obsolete, or represented by wrinkles or coarse striee. 

 They are present on the anterior surface of the jaw only, or 

 on both anterior and posterior surfaces. They are distant, 

 narrow, stout, few, or crowded, broad, stout and numerous. 

 Their number is inconstant in the same species. They some- 

 times are very broad, and seem like separate plates soldered 

 to the anterior surface of the jaw, or to be formed by a 

 folding of the jaw upon itself. When this appearance of 

 folding into plaits is given it will generally be found that the 

 plait-like sections are actually separated by distinct, but 



* Hence, probably, Draparnaud correctly reports its presence in Helix algira. 



