24 THE NAUTILUS. 



the shell. On the whole, the fossil individuals appear to be 

 more variable than the recent forms. The variations in cari- 

 nation have been recognized to some extent and names have 

 been applied to the most striking of these variations. Seven 

 combinations are apparently possible. These are indicated in 

 the following table : 



Tricarinate tricarinata Say. 



Middle carina absent perconfusa Walker. 



Upper and lower carinae absent umcarinata, DeKay. 



Lower carina absent basalis Vanatta. 



Middle and upper carina absent infracarinata Vanatta. 



Middle and lower carina absent supracarinata Baker. 



All carinae absent simplex Gould. 



VALVATA TRICARINATA SUPRACARINATA n. var. 



Shell differing from the other described varieties of the 

 tricarinate series in lacking the carina on the periphery and 

 base. Otherwise similar. Length, 3.5; width, 4.5; aperture 

 length, 2.0 ; width, 1.8 mm. Topotype, Collection Museum of 

 Natural History, U. of I., No. P928. Type locality, near 

 Morris, Grundy County, Illinois. 



This variation is apparently rare, as but four specimens 

 were found in sorting several hundred tricarinata. In the 

 deposit under study (Grundy County) the perconfusa form 

 was in much greater abundance, followed by the tricarinata 

 form. See NAUTILUS, XV, p. 124; XXXI, p. 36; XXVIII, 

 pp. 104, 105, for descriptions of the other variations of this 

 polymorphic species. 



SOME CENTRAL AMERICAN SPECIES OF NAIDES, BELONGING OR 

 ALLIED TO THE GENUS ELLIPTIC. 



BY A. E. ORTMANN, PH. D. 



Frierson (NAUTIL. 27. '13, p. 14) has described a new species 

 as Unio (Nephronaias) ortmanni, and says that it "is clearly 

 placed in the Nephronaias division by its evident near kinship 

 to melleus Lea and to persulcatus Lea ". 



