Ortmann: Families and Genera of Najades. 



289 



bu1 septa more irregular in the non-marsupial gills. In the marsupial 

 gill of the female, the septa are crowded, even more so than in .1. 

 cygnea. The tissue of the gills is generally more delicate in . 1. com- 

 planata, bul the various elements are similar to those of A. cygnea. 

 The glochidia (see Plate XIX, fig. 3, also Schierholz, 1889, pi. 2, tig. 29; 

 Fleming, 1875, pi. 3, fig. 11) are smaller, longer than high, with shorter 

 hooks; thus the outline is less distinctly triangular, and less pointed. 

 I find the length to be 0.34, the height 0.32; while Haas (1910a) gives 

 0.33 mm., but does not say in which dimension. 



For this species, Bourguignat (1880, pp. II-13) has created the 

 genus Pseudanodonta, founded originally upon the shape of the shell 

 and differences in the hinge. The first character is quite pronounced, 

 but cannot be regarded under any condition as a generic character; 

 the second does not exist at all, which is best shown by the fact that 

 it has been dropped entirely by subsequent authors (Haas). Other 

 writers have added to the distinctive characters, which have been 

 condensed by Haas (1910a, p. no; and 

 1910c, p. 170). According to Germain, the 

 beak-sculpture is said to be different. 

 Pseudanodonta is reported to have three to 

 five tubercular ridges, which are absent in 

 the true Anodonta, while in Anodonta, there 

 are flexuous ridges, but never tubercular 

 ridges ("les Pseudanodontes ont . . . trois 

 a cinq rides tuberculeuses . . . qui man- 

 quent chez les veritables Anodontes. Chez 

 les Anodontes, les sommets sont parfois 

 ornes de rides flexueuses, mais jamais de 

 rides tuberculeuses"). This statement is an 

 intentional exaggeration of the actual con- 

 ditions, worded with the purpose to obscure 

 the similarities, and to emphasize the differ- 

 ences. The fact is that in both Anodonta 



and Pseudanodonta, the beak-sculpture is of the same type, and 

 consists of a number of double-looped bars, of which, in com planata, 

 the posterior loop is slightly more swollen, but not tubercular. Haas 

 also described the beak-sculpture of Pseudanodonta as "consisting ol 

 a fejv isolated, rather elevated tubercles," which is positively wrong, 

 as is shown by the specimen- before me. 



mp 



Fig. \\u. Left gills of a 

 sterile female from same lo- 

 cality. 



