THE NAUTILUS. 137 



Of the seven possible variations from the normal arrangement, 

 but four were noticed. In no case were the cardinals alone reversed,' 

 but invariably a reversal of these teeth was accompanied by a 

 reversal of either one or both pairs of laterals. Neither were'the 

 cardinals and posterior laterals alone, nor both pairs of laterals 

 alone reversed in any case. The following table gives the details of 

 the different variations observed and their relative frequency. 

 Normal Sphferium cardinals .1 Ant. Lat. j Post. Lat. j. 

 Abnormal S. striatiimm Lam. 



No. of specimens 22: Cardinals i Ant. Lat i Post. Lat. }. 

 No. of specimens 32: Cardinals f Ant. Lat. i Post. Lat. f. 

 No. of specimens 2'2: Cardinals f Ant. Lat. J Post. Lat. i. 

 No. of specimens 32 : Cardinals \ Ant. Lat. f Post. Lat. \. 

 Abnormal .S'. simile Say. 



No. of specimens 52 : Cardinals f Ant. Lat. 3 Post. Lat. f 

 No. of specimens 32: Cardinals f Ant. Lat. j Post. Lat. J. 

 No. of specimens 22 : Cardinals J Ant. Lat. \ Post. Lat. J. 



NEW AMERICAN ANCYLIDJE. 



BY HENRY A. PILSBRY. 



Owing doubtless to the difficulty of distinguishing species in this 

 group, but little work has been done upon the United States forms 

 since the publication of Haldenmn's monograph in 1842. Clessin, 

 in the "Conchylien Cabinet," has added nothing of value to our 

 knowledge of United States species, his A. oregouensis from Salem, 

 Oregon, of which I have " topotypes," being doubtfully distinct from 

 Tryon's A.fragilis. A. caurinus is also, as Tryon states, a synonym 

 vffragilis. 



In naming a series of Illinois mollusks for the Illinois State Lab- 

 oratory of Natural History, my attention was directed to this genus. 



The species of Ancylm fall into two groups, not, I suppose, of 

 much importance systematically, but of considerable interest in a 

 broad view of the conditions of mollusk life. One group, which 

 may be termed the " petrophilous " Ancyli, live on rocks and shells 

 in rivers, and usually have a rather highly conic shell. The other 

 group, " phytophilous " Ancyli, live on water plants ; some deeply 

 submerged, as on the " leaves of grass " (to use a Walt, Whitman- 

 ism), streaming upward from the bottom ; others inhabit the round 



