ORTMANN: FAMILIES AND GENERA OF NAJADES. 263 
Structure of the soft parts like those of the following species, which 
see. Color of soft parts also of similar type. Mantle-connection 
separating anal and supra-anal very short. Anal with fine crenula- 
tions, branchial with papillae. Posterior margin of palpi connected 
for about one-half of their length. 
Gills of the usual structure, in the female only the outer gills are 
marsupial (see Plate XVIII, fig. 2). 
In the soft parts there are no characters which assign this species 
to a definite genus, except that they indicate, that it is not Fusconaja 
and not Quadrula. It has been placed by Simpson in the latter genus. 
In the shape of the shell it most resembles the coccineum-obliquum- 
group of Pleurobema, from which it is distinguished by the rather 
distinct posterior ridge. I think, P.riddelli comes in here, but stands 
rather isolated by itself. The dark color of the epidermis is also un- 
usual in this genus. 
Pleurobema coccineum (Conrad). 
Numerous specimens have been examined from the smaller creeks 
of the Ohio and Lake Erie drainage in western Pennsylvania, among 
them some fifty gravid females. The species is tachytictic, and the 
breeding season lasts from the end of May to the end of July. 
The soft parts have been described by Simpson (in Baker, 1898, 
p- 79), but the account given of the marsupium is wrong. 
Margin of the mantle, branchial, anal, and supra-anal openings of 
the usual conformation, as also the gills and palpi. Branchial with 
papilla, anal with distinct, almost papille-like crenulations. The 
mantle-connection between the anal and supra-anal was found absent 
in some cases. Posterior margins of palpi connected for one-half, or 
even more, of their length. 
Only the outer gills are marsupial.’ When gravid, the outer gills 
swell only moderately, the edges remaining sharp. The ovisacs are 
compressed and lanceolate and the placenta, which are distinctly 
developed, have the same leaf-like shape; they are always white, and 
are permanent, being discharged whole. This discharge has been 
observed several times. Glochidia rather small, subovate, without 
15 Lefevre and Curtis (1910, p. 83) suggest that the fact that I found only the 
outer gills charged may be due toa partial discharge of the marsupia in consequence 
of beginning suffocation. This supposition is untenable. I observed many speci- 
mens in the field. Moreover, even in females, which have the marsupium not 
charged, it is easily seen that only the outer gills have marsupial structure. 
