NORTH AMERICAN SPECIES OF THE GENUS ATAX 241 



This species was first identified from a specimen collected at 

 "26 " Lake, near Charlevoix, Mich., f rom Anodonta Jragilis, 

 and another collected at Intermediate Lake, Ellsworth, Mich., 

 also from A. fragilis. Koenike described it from that species 

 and from Unio coniplanatus. 



It seems to be found in both Unio and Anodonta, as at 

 Grand Rapids, Mich. , it has been collected in Unio gibbosus, 

 U. ligamentinus and Anodonta footiana. In one specimen of 

 A. footiana were 23 irregular masses of eggs, varying from 

 1.0 to 2.5 mm. in diameter, and in various stages of develop- 

 ment, with one mite 2.0 mm. long and another, a female full of 

 eggs, 6.0 mm. in length. At Long Lake, Kalamazoo, Mich., 

 one male has been taken from U hcteolus. Only 16 speci- 

 mens have been found altogether, so it seems, like A. titmidus, 

 to be a rare species. 



SYNOPSIS OF THE SPECIES INCLUDED ABOVE. 



Genital field toward the end of the body and 

 in general form more or less broadly oval 

 or approximately circular; females with va- 

 riously modified spines about the genital 

 opening which assist in oviposition, the 

 eggs being deposited singly in the gills, 



(Atax) 2. 



Genital field removed from the 

 end of the body, immediately behind the 

 last epimera and plates so extended trans- 

 versely as to have the form of very low 

 broad triangles, whose long bases extend 

 from either side of the genital cleft a con- 

 siderable part of the .way toward the side 

 of the body. No spines at genital opening, 

 the eggs being laid in masses between the 



gills (Najadicola) 13 A. (iV.) ingens (Koen.) 



Acetabula 6 on each side in two groups of 



three each 3. 



16 



