THE MOLLUSCA IOOI 



119(118,120) Shell spinose Section Canthyria Swainson 



The typical and only species, 

 Unio spinosus Lea (Fig. 1490; 

 X 1). is confined to the Altamaha 

 River, Georgia, and is one of the 

 most remarkable Unios known. 

 In the extraordinary develop- 

 ment of the spines, it is unique. 



FIG. 1490. 



120 (118, 119) Shell smooth; beaks sculptured with concentric ridges. 



Section Uniomerus Conrad. 



The typical species, Unio tetralasmus 

 Say (Fig. 1491; X 5), has a wide range 

 from Ohio south to Alabama and Texas. 

 A few other species are found in Georgia 

 and Florida. 



FIG. 1491. 



121 (107, 140) Marsupium formed by the entire outer gills, distending trans- 



versely, when charged; water tubes in the gravid female 

 divided longitudinally into three tubes, of which only the 

 center one is used as an ovisac. Hinge rarely complete, the 

 laterals or both the pseudocardinals and laterals being often 

 entirely wanting; sexual differences in the shell very rarely 



present Subfamily ANODONTINAE . . 122 



Eleven genera: 122, 123, 124, 125, 126, 127, 128, 129, 130, 134, 139. 



122 (123) Hinge with lateral teeth wanting and only rudimentary pseudo- 



cardinals; beak sculpture consisting of a few strong, con- 

 centric ridges. Ovisac of each water tube subdivided into 

 a number of compartments running crosswise to the gill. 



Strophitus Rafinesque. 



Only a few species are known, most 

 of them coming from the Southeast- 

 ern States. The species figured, S. 

 edentulus Say (Fig. 1492; Xl), has a 

 wide range from New England to 

 North Carolina and west to Minne- 

 sota and Tennessee. 



FIG. 1492. 



