ORTMANN: FAMILIES AND GENERA OF NAJADES. Sol 
Marsupium kidney-shaped, swollen, formed by many ovisacs, occupy- 
ing the posterior part of the outer gill. Edge of marsupium blunt, 
projecting beyond the original edge of the gill, beaded, often pig- 
mented. Placente not solid. Glochidia subovate, of medium size, 
or rather large. 
Type E. recta (Lamarck). 
This genus represents typically that group of the Lampsiline, in 
which the aération of the glochidia is regulated by special structures 
on the edge of the mantle in the shape of papilla. These papille 
show several distinct types of arrangement, and according to them 
(together with other characters) subgenera may be distinguished. 
1. Subgenus Carunculina Simpson, 1898 (see Simpson, 19008, p. 563). 
On the edge of the mantle, in front of the branchial, a rather short 
group of crowded papilla, resembling a caruncle. Inner lamina of 
inner gills more or less free from abdominal sac. Beak-sculpture 
concentric, rather distinct, bars curving up behind and somewhat 
angular. 
Type E. parva (Barnes). 
The beak-sculpture is so peculiar in these forms that Carunculina 
might be entitled to generic rank. 
2. Subgenus Micromya Agassiz, 1852 (see Simpson, 1900), p. 524). 
On the edge of the mantle in front of the branchial there is a shorter 
or longer row of rather irregular, larger and smaller papilla, reaching 
not quite to the middle of the lower margin. Inner lamina of inner 
gills connected with abdominal sac, or more or less free. Shell small, 
or of medium size, subovate, or subelliptical, not very long, and not 
much pointed behind. Beak-sculpture distinctly sinuated or double- 
looped, but often obsolete; the posterior loop often showing a tendency 
to be open. 
Type E. fabalis (Lea). 
Simpson has two species in his genus Micromya, M. fabalis and 
celata (Conrad). The anatomy of the latter is unknown. The type- 
species has a structure essentially identically with a number of species, 
which stand in Simpson’s Lampsilis. Since the latter name is used 
here in another sense, the name Micromyva becomes available for this 
assemblage of species. . 
