Ortmann: Families and Genera of Najades. 2G3 



Struct urc of the sofl 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 

 mat>tipial (see Plate XYIII, 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 Quadnda. ft has been placed by Simpson in the latter genus. 

 In the shape of the shell it most resembles the coccineum-obliquuni- 

 group of Pic a robe ma, from which it is distinguished by the rather 

 distinct posterior ridge. 1 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 papillse-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. 15 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 to a 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. 



