/O THE NAUTILUS. 



48. Pomatiopsis lapidaria Say. Common. 



49. Carychium exiguum Say var. exile Ad. Few. 



50. Heiicina orbiculata Say. Common. 



ON A REVISION OF THE AMERICAN UNIONID^. 



CHAS. T. SIMPSON, WASHINGTON, D. C. 



In looking ovei' the September ISTautilus I was greatly interested 

 in the article on American Association of Conchologists, and heartily 

 agree with the suggestion that the nomenclature of our American 

 Unionidfe needs revising. But to do this properly will be an her- 

 culean labor, one that will require time, hard study, and infinite 

 patience, as well as a love for the work. 



In the first place most of the literature on the subject is out of 

 print, and much of it, such as the New Harmony Disseminator, 

 Nicholson's Encyclopedia and the like, is so rare as to be practically 

 out of the reach of the average student. It is scattered in a very 

 large number of publications and it will take a considerable amount 

 of careful research to hunt up what has been written on the subject. 



Much of this literature is in a terribly confused condition, and there 

 are many disputed points which will require the nicest judgment to 

 satisfactorily settle. Lea read the descriptions of most of his species 

 before scientific societies, claiming that such reading was a bona fide 

 publication, and dated them from that time ; Conrad held that no 

 species could be considered published until a description had been 

 printed and circulated. There was a further dispute between them 

 as to dates. Lea holding that of publication of the part or separata 

 in which his descriptions were printed was valid, Avhile Conrad 

 claimed that the date should be given when the whole volume was 

 issued. There are many disputed points between Say and Lea as to 

 their species. Lamarck described his Unionidse in Animaux sans 

 Vertebres, in Latin, giving each S23ecies from ten to fifteen words, 

 without figures, and their identification largely rests on the fact that 

 Dr. Lea afterwards examined the types. 



Rafinesque, in his ]\Ionograph of the Bivalve Shells of the Ohio 

 River, described and figured a large number of Unionida?, but the 

 descriptions are brief and unsatisfactory, and the figures are unrecog- 

 nizable. Certain conchologists have considered his work valid, and 



