ORTMANN: FAMILIES AND GENERA OF NAJADES. 257 
Although the shape of the shell is very unique in this species, it 
clearly belongs to the metanevra-group, as has been recognized already 
by Simpson, and the soft parts bear out this affinity, since they are 
identical in all essential characters. Of course, according to the shape 
of the shell, the gills are 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 
that 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, 1900), 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, 
