SYNOPSIS OF THE tfAlADES, OE PEARLY FRESH-WATER 



MUSSELS. 



By CHARLES TORREY SIMPSON. 

 Aid, DirixiuH <>/ Mollusks. 



In 1836 Dr. Isaac Lea published a Synopsis of the Family of Nai- 

 ades, which was followed by a second edition in 1838, a third in 1852, 

 and a fourth in 1870. In this work Dr. Lea did not attempt to make 

 any systematic classification, but divided the species into two great 

 genera, Margaron and Platiris, and subdivided these genera into sub- 

 genera, and finally into smaller groups founded on the presence or 

 absence of a dorsal wing, and on the form and sculpture of the shell. 

 This arrangement was regarded by Dr. Lea as merely a temporary one, 

 to be used until a knowledge of the soft parts could be obtained, on 

 which to base a permanent classification. 



Several other attempts at a classification of the Xaiades have been 

 made, and among these is that of Swainson in 1840, who believed that 

 the whole family formed a circular group, that by beginning at a cer- 

 tain point in it the species or genera would be found closely related to 

 others, and these to others still, and that by following up the chain of 

 relationships one would be brought back to the place of starting. My 

 studies have not borne out Swainsoirs conclusions, but I have adopted 

 two of his divisions of the Unionida?, the subfamilies Uniouiune and 

 Hyrianae. His subfamilies Anodontinre and Alasmodontina? have no 

 value, and the subfamily Iridina' belongs in the family Mutelida'. 



In 1847 Gray gave a classification of the Xaiades in his List of Recent 

 Genera, in which he divided them into three families: Unionida', with 

 the genera Anodonta, Maryaritana, Monocondylcea, Unio, Barbala, Lam- 

 proscaplia, Anodonta, Byssanodonta, and Glabaris; Mutelida- with 

 Mutela, Leila, Pleiodon, Paxyodon and Prisodon, aud Mycetopodidre, with 

 the genus Mycetopus. 



Troschel, in 1847, proposed a classification in which the genera were 

 founded on anatomical characters, and though for lack of knowledge 



PROCEEDINGS U. S. NATIONAL MUSEUM, VOL. XXII, No. 1205. 



