280 Annals of the Carnegie Museum. 



connection between anal and supra-anal moderately long. No tendency 

 to unite the inner lamina of inner gills with abdominal sac. . Anodontoides. 

 03. Beak-sculpture concentric, heavy. Mantle-connection between anal and supra- 

 anal moderate. Certain forms with tendency to connect the inner 

 lamina of inner gills with abdominal sac. 



bi. Ilinge-teeth more or less developed, at least the pseudocardinals present. 

 Marsupium with simple ovisacs. Shell subrhomboidal. . . Alasmidonta. 



h. Hinge-teeth rudimentary. Marsupium of gravid female unknown. Shell 

 elongated Lastena. 



bs. Hinge-teeth rudimentary. Marsupium with ovisacs subdivided into trans- 

 verse compartments. Shell subovate Strophitus. 



The most primitive types are undoubtedly Symphynota and Alas- 

 midonta, and among them species with fully developed hinge-teeth 

 are found. The most extreme modification of the soft parts is seen 

 in Strophitus, while the most extreme specialization in the shell is 

 represented by Anodonta (most successful adaptation to the life in 

 quiet water with muddy bottom). Arcidens is peculiar in its shell 

 sculpture. Anodontoides is a connecting form between cii and 03, 

 but with the whole shell-structure more inclining toward ci\. Lastena 

 is yet rather doubtful in its position. 



It must be pointed out that comparatively few forms have been in- 

 vestigated, and that further knowledge will possibly furnish the means 

 for a better understanding of the phylogeny of this subfamily. There 

 surely should be Anodontince in Asia (aside from Anodonta proper), 

 which possibly might be more primitive than any of those investigated 

 hitherto. For the present, the most ancient types are known from 

 North America, but I do not think that the subfamily originated in 

 this continent. The shape of the glochidia indicates, that it started 

 probably from a form near the European genus Unio, and this makes it 

 more likely that the ancestral form lived in the Old World. 



Genus Symphynota Lea. (1S29.) 

 (Simpson, 19006, p. 662.) 



Shell ovate or elliptic, compressed, with smooth disk, but sometimes 

 with ribs upon the posterior slope. Beak-sculpture distinct, consisting 

 of a few concentric bars, followed by others, which are distinctly 

 sinuated, 25 or double-looped. Hinge with teeth, the pseudocardinals 

 always present, the laterals present, imperfect, or absent. 



Soft parts of typical structure: outer gills alone marsupial, when 



25 See description of beak sculpture of 5. costata. 



