ORTMANN: FAMILIES AND GENERA OF NAJADES. 335 
Inner lamina of inner gills free from abdominal sac, except at an- 
terior end. Inner edge of mantle in front of branchial, with a series 
of rather distant, thin, but long, papilla, resembling thick hairs. Mar- 
supium formed by comparatively few ovisacs (six to eight), swollen, 
kidney-shaped, and occupying only a small part of the outer gill, im- 
mediately behind the middle. Ovisacs rounded at the end, projecting 
beyond the edge of the gill, not very sharply marked off from each 
other. Placentz not solid. Glochidia subovate. 
Type M. conradicus (Lea). 
This isa doubtful genus. The description of the marsupium of 
M. parvulus (Lea, Obs., XI, 1867, p. 45) is similar to that of the type- 
species. In M. penicillatus, Lea (Obs., VII, 1860, p. 203) describes 
the marsupium as larger, but in a foot-note he mentions that in 
another specimen it was as small as that of conradicus. In M. 
acutissimus, the marsupium occupies, according to Lea (Obs., X, 1863, 
p. 411), the whole length of the gill. Simpson also says in the generic 
diagnosis, that the marsupium sometimes extends nearly the whole 
length of the gill. If thus the shape of the marsupium as described 
above should be inconstant, the most important generic character 
would be taken away, and Medionidus would fall as a synonym under 
Eurynia, with which genus it is indeed closely related in all other 
respects. Possibly in this case it would be best to make it a subgenus 
of Eurynia, on account of certain other peculiarities, such as the free 
inner lamina oi the inner gills and the shell-sculpture. 
Medionidus conradicus (Lea). 
A male and a gravid female have been sent me by B. Walker, from 
the South Fork of the Cumberland River, Burnside, Pulaski Co., 
Kentucky. 
Anal and supra-anal separated by a mantle-connection of medium 
length. Anal crenulated, branchial papillose. In front of the branchial 
the edge of the mantle carries in the female distinct, long, slender, hair- 
like papille almost as far forward as the middle of the lower margin. 
These papillez are also present in the male, but considerably shorter. 
Palpi with the posterior margins connected at the base. 
Diaphragm and gills of usual shape. Marsupium small, consisting 
of six to eight indistinctly separated ovisacs, forming an almost 
globular swelling just behind the middle of the outer gill. Glochidia 
rather large, subovate, or almost subspatulate. Length 0.22; height 
0.28 mm. (see Plate XX, fig. 3). 
