124 THE NAUTlLUb. 



subject to variation than at the present time. In the NAUTILUS, 

 XI, p. 121, will be found an account of several specimens in which 

 an additional carina was developed. In a large amount of material 

 from the marl deposits of the State recently examined, two examples 

 were found in which the superior and peripheral carinae are present, 

 but the basal one is obsolete, while in a deformed specimen from 

 the deposits at White Pond, N. J., only the basal one is present. 

 Two specimens from Michigan marl deposits have the last whorl 

 near the aperture, entirely separated from the body whorl. None of 

 these variations have been noticed so far as I am aware in recent 

 specimens. In the collection of the late Dr. Jas. Lewis, now in my 

 possession, is a sinistral specimen (fig. 4). 



As these variations occur only in very few instances, they are to 

 be classed as individual variations or " sports," rather than as dis- 

 tinct forms worthy of varietal names. 



Var. confusa n. v. (fig. 2). Body whorl bicarinate, peripheral 

 carina obsolete ; periphery rounded or angulate. Valvata tricarinata. 

 var. bicarinata, authors generally, not of Lea. A curious scalariform 

 specimen is in the collection of Mi-. J. II. Ferriss, of Joliet, 111. 



(fig- 3). 



Var. unicarinata DeKay. Unicarinate, peripheral and basal 

 carinaj obsolete, periphery rounded, base rounded or angulate. 

 Valvata unicarinata DeKay. N. Y. Moll., p. 118, pi. VI, f. 129 

 (1843). 



Var. simplex Gld. Ecarinate, whorls usually more or less flat- 

 tened above. Valvata tricarinata var. simplex, Gld., Invert Mass., 

 p. 226, f. 126 (pars.), (1841). 



The citations of Valvata humeralis Say from Michigan by Miles 

 (Geo. Sur. Mich., p. 237, 1860) and from Canada by Bell, 

 Whiteaves, etc., referred to by Binney (L. & F. "W. Shells, III, 

 p. 14), are in all probability based upon this form. 

 II. Valvata bicarinata Lea (fig. 6). 







Shell discoidal, flattened above, rather thick, shining ; horn- 

 colored or tinged with green ; whorls 3^, shouldered, upper surface 

 sloping downward from the carina to the suture, which is deeply im 

 pressed ; spire greatly depressed, not rising above the carina of the 

 body whorl when viewed from in front; lines of growth faintly 

 marked ; body whorl bicarinate, superior carina revolving nearly to 

 the apex, periphery rounded or bluntly angulate ; carina? sharp. 



