22 THE NAUTILUS. 



toward the faces of the gill, are developed during the breeding sea- 

 son, while only the central part of each original water-tube is used 

 as ovisac. The ovisacs are closed also at the base of the marsupium. 

 Glochidia rather large, subtriangular, with hooks. — These forms 

 have a long breeding season. 



Also of this subfamily, the typical genus is European, and the 

 type-species is Anodonta cygnea (Linnaeus) of Europe. 



Anodonta cygnea (Linnaeus). I have a large number of speci- 

 mens, of both sexes, the females sterile or gravid, with eggs as well 

 as with glochidia, in my hands. They represent various forms of 

 this polymorphous species (piscmalis, Jluviatilis, anatina, cellensis 

 etc.), but I agree with certain European writers in regarding them 

 all as one species. At any rate, in the anatomical structure, they 

 are all alike. 



The soft parts of this species correspond to the characters given for 

 the subfamily above in every detail, and it is not necessary to describe 

 them again, except to make the statement that the anal and supra- 

 anal openings are separated by a very long interval. It may also be 

 mentioned that I possess slides of this species, which show the for- 

 mation of the lateral water tubes of the marsupium most beautifully, 

 rendering it beyond doubt that these tubes are actually cut off from 

 the original water-tubes.^ 



Anodonta complanata Rossmaessler. I have six specimens from 

 Bavaria, among them two males, one sterile, and three gravid fe- 

 males, the latter with glochidia. 



The structure of the soft parts is absolutely like that of A. cygnea 

 in all essential points. For this species the genus Pseudanodonta has 

 been created by Bourguignat, which recently has been taken up as 

 valid by Haas (Najadenfauna des Oberrheins, in: Abh. Senckenberg. 

 Naturf. Ges. 32, 1910, p. 170, and Pr. Malacol. Soc, g., 1910, p. 

 110). The characters originally given by Bourguignat, and added 

 to by Germain (see Haas), are taken from the shell, and, aside from 

 the compressed shape of the latter, are entirely imaginary. Later 

 on, the shape of the glochidia was added (Schierholz) as a further dif- 

 ference, and (by Clessin) the structure of the gills, in terms which 



1 An epithelial fold each on two opposing faces of two septa grows into the 

 lumen of the water-tube, and these two folds come into contact. In this spe- 

 cies I have not seen them firmly united, as in other species, although this un- 

 doubtedly will be the case when they are tuUy developed. 



