Z AMERICAN COREICULAD^E. 



B. Cardinal teeth 2, 2, moderately diverging, front of right valve and 

 hinder of left valve smaller ; lateral teeth elongate, compressed, smooth ; 

 of right valve double, of left valve simple. Shell thin. 



5. Sphaerium, SCOPOLI, 1777. Shell oblong, cordate, equilateral; 



syphon of animal separate, diverging at the tip. 



6. Pisidium, PFEIFFEK, 1821. Shell ovate, wedge-shaped, inequi 



lateral, truncated behind ; syphons of animal short, united to 

 the end. 



CORBICULA, MEGERLE. 1 



Tellina, MULLER, 1774. Venus, CHEMN. 1782. Cyclas, BKUG. 1792. 

 Corbicula, MEGERLE, 1811. Cyrena, LAMK. 1818. Venulites, 

 SCHL. 1820. 



Animal. &quot; Mantle, lobes free on the lower edge and in front, 

 united behind ; edge simple, with a series of short conical beards 

 just within the margin ; syphons two, very short, separate, con 

 tractile ; apertures fringed with short crowded conical beards ; 

 foot compressed, subquadrate, rather produced in front ; body 

 swollen ; abductor muscles large, anterior oblong, the hinder 

 round, subtrigonal. 



&quot; Labial tentacles 2 pair, large, broad, trigonal, equal ; gills 

 oblong, inner pair large, the outer about half the depth of the 

 inner.&quot; GRAY, MSS. 



Shell oval or trigonal, subequilateral, heart-shaped ; three 

 diverging cardinal teeth in each valve ; two lateral teeth com 

 pressed, narrow, very finely striated ; beaks generally broad and 

 not much raised ; muscular impressions small, round, or elliptical ; 

 palleal impression variable. 



This genus was instituted by Megerle 1 for a certain group of 

 fresh-water bivalves, placed by Miiller among the Tellina, and 

 represented by the Tellina fluminalis, fluviatilis, and fluminca. 



The Corbicula diifer from the Cyrena proper, in havfng the 

 lateral teeth very much elongated, narrow, both of nearly the 

 same size, and very finely striated. The species of this genus are 

 trigonal, and are, with the exception of Corbicula woodiana, 

 as compared to the Cyrena, always small. The animal is similar 

 to that of Cyrena. 



i Berliner Mag. V, 1811, 56. 



