Ortmann: Families and Genera oi Najades. 257 



Although the shape of the shell is verj unique in this species, il 

 clearlj belongs to the metanevra-group, as has been re< ovmi/ed ahead \ 

 by Simpson, and the sofl parts bear oul this affinity, since thej are 

 identical in all essential characters. Of course, according to the shape 

 of the shell, the gills arc very long and narrow. The mantle connection 

 between anal and supra-anal was always found present. The inner 

 edge of the anal is practically smooth. The posterior margins of the 

 palpi are united for about one-half of their length. 



All four gills have a marsupial structure in the female, and the inner 

 gill has the water-tubes a little wider in the basal part than the outer 

 gill. No gravid specimens have been found. 



The color of the soft parts of this species is very remarkable. The 

 general ground color is yellowish orange, with black markings. The 

 abdominal sac is whitish, with blackish gray markings, chiefly pos- 

 teriorly. The foot is grayish at the extremity, shading into black, The 

 black ending in a sharp horizontal line, which is followed by grayish 

 orange. The palpi are yellowish, with a gray edge, the gills are grayish 

 brown, the mantle transparent gray, shading to grayish yellow on 

 the margin, with a blackish brown edge, which becomes deep black 

 and very wide posteriorly at the siphons. The adductors are pale 

 yellowish to orange. The color varies in different specimens in so far 

 thai in some the ground-color is paler yellow, while in others it is of a 

 more intense yellow, inclining to orange. 



Breeding season and glochidia unknown. 



Genus Rotundaria Rafinesque. 1820. 

 Simpson, n)oob, p. 794 (as subgenus). 



Shell rounded or quadrate, with elevated beaks, very deep beak- 

 cavities, and well developed hinge-teeth. Outer surface sculptured 

 with tubercles and nodules. Epidermis brown, without rays. Beak- 

 sculpture consisting of numerous rather close bars, the first few con- 

 centric, those following developing a strong angular loop on the 

 posterior ridge, and an anterior loop, which soon breaks up into an 

 irregular zig-zag pattern of more or less isolated tubercles. This 

 sculpture extends somewhat upon the disk and mingles with the first 

 tubercles of the disk. Nacre more or less violet, which may be a 

 specific character. 



Soft parts primitive in structure. The anal is never closed above, 



