286 Annals of the Carnegie Museum. 



Genus Anodonta Lamarck. (1799.) 

 Simpson, 19006, p. 620. 



Shell elliptical, or elongated; thin; flat, or inflated, with smooth 

 disk. Beak-sculpture distinct, but not very heavy, of the double- 

 looped type, the loops separated by a sinuation, or a reentering angle. 

 Hinge-teeth completely absent. 



Only the outer gills are marsupial. When charged, the edge dis- 

 tends, and secondary water-tubes are present. Ovisacs not sub- 

 divided. No placenta? are developed. Inner lamina of inner gills 

 free from abdominal sac. Mantle-connection between anal and 

 supra-anal generally very long, longer than either opening. 



Type A. cygnea (Linnaeus). 



In the reduction of the hinge-teeth, in the long mantle-connection 

 between anal and supra-anal, and the whole structure of the shell, 

 this genus represents a very extreme specialization of the anodontine 

 type. In the free inner lamina of the inner gill it is rather primi- 

 tive. 



A large number of species are recognized by Simpson (19006), but 

 in Europe the species-making in this group has gone beyond all the 

 bounds of reason. A healthy reaction is, however, setting in, with 

 regard to this genus as well as the European genus Unio (see Kobelt, 

 1908, p. 91; Thiele, 1909, p. 33; Israel, 1909, p. 26; Haas, 1910c). 

 As will be shown below, the European genus Pseudanodonta, which 

 has been split off, is also unsatisfactorily supported. It remains to 

 be seen, whether the species from western North America and Asia 

 have the same structure of the soft parts. Certain Chinese forms 

 differ in the beak-sculpture. 



Anodonta cygnea (Linnaeus). 

 See also Ortmann, 1911c, p. 22. 



A large number of specimens of both sexes, including gravid females, 

 from various places in Germany and Hungary have been sent to me 

 by W. Israel. 



I agree with Israel (1909) in regarding all Anodontas of central 

 Europe (except complanata) , as one species. The form cellensis is 

 surely only the senile form of ponds, and anatina is the form of small 

 creeks. The name of this species should be cygnea and not piscinalis. 



