Ortmann; Families and Genera of Najades. 337 



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. Placent;e not solid. Glochidia subovate, of medium >i/e, 

 or rather large. 



Type E. recta (Lamarck). 



This genus represents typically that group of the Lampsilince, in 

 which the aeration of the glochidia is regulated by special structures 

 on the edge of the mantle in the shape of papilla?. These papillae 

 show several distinct types of arrangement, and according to them 

 (together with other characters) subgenera may be distinguished. 



I. Subgenus Carunculina Simpson, 1898 (see Simpson, 19006, p. 563). 



On the edge of the mantle, in front of the branchial, a rather short 

 group of crowded papillae, 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. parca (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 papillae, 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 

 ccelata (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 Micromya becomes available for this 

 assemblage of species. 



