Zoology 735 



The census thus taken revealed no less than eight hundred 

 and twenty-nine nominal species of gastropods inhabiting the 

 United States. The aggregate of the species known at the 

 present day is not very much greater, and the figure is too 

 large for at least one family that of the " Pleuroceridae," or 

 American Melanians. 



The bivalves could not be treated in the same manner as 

 the gastropods. There are only three families represented 

 in the United States, but one of them the Unionidae is 

 an immense assemblage of species, and no one could be found 

 willing to undertake the task of monographing them. The 

 other families Cyrenidae and Pisidiidae were then uni- 

 versally combined in one, and in 1865 were treated by 

 Temple Prime in a " Monograph of the American Corbicu- 

 ladse (recent and fossil)." In this monograph one hundred 

 and eleven species were recognized, of which ninety-three 

 belong to the family Cyrenidae and eighteen to the family 

 Pisidiidae. In these numbers, however, are embraced not 

 only the recent species of temperate and cold North America, 

 but also those of the warm regions and South America, as 

 well as the extinct species. Reduced within the limits cov- 

 ered by the other monographs, the numbers were as follows : 



Cyrenidae 32 Pisidiidae 12 



A small monograph, evoked by the differences of opinion 

 respecting questions considered in the " proof" of the third 

 part of the " Land and Fresh-water Shells of North Amer- 

 ica," was published meanwhile (in 1865) by Doctor William 

 Stimpson, and embraced the results of anatomical studies, 

 especially of the lingual ribbon, of the Hydrobiids. 



In 1885 Mr. Binney resumed a consideration of the ter- 

 restrial Pulmonates in " A Manual of the American Land 

 Shells." This is the volume already alluded to in connection 



