220 robeet h. wolcott: 



The legs of the female are slenderer and relatively shorter and III much 

 shorter than in the male. IV, 4 is exceeded by both 5 and 6. There is no 

 marked structural peculiarity; the segments of the last pair decrease reg- 

 ularly in thickness from 1 to 6; IV 4 lacks the six large spines; and IV 5 

 the two long ones, retaining the row of spines on the flexor surface. 



The genital area of the male lies one-half on either side of the groove 

 in the emarginate posterior end of the body, the opening being at its bot- 

 tom; the latter is bounded by two rather broad lunular plates, each with five 

 acetabula in two groups — two in front and three behind. In the female a 

 transverse division indistinctly separates each of these lunules into two 

 parts, the anterior with two, the posterior with three acetabula, and each 

 bears at the angle adjacent to the other three, a flattened spine. 



measurements: 



Female Male 



Length of body 0.714 mm. 0.586 mm. 



Length of leg 1 0.560 mm. 0.510 mm. 



Length of leg II 0.740 mm. 0.688 mm. 



Length of leg III 0.663 mm. 0.668 mm. 



Length of leg IV 0.770 mm. 0.745 mm. 



Palpus 0.306 mm. 0.265 mm. 



Mandible 0.178 mm. 0.153 mm. 



Types in the author's collection; co-types have been deposited in the 

 collection of the Zoological Laboratory, University of Nebraska, in the 

 Museum of Comparative Zoology, of Harvard University, in the United 

 States National Museum, and in the Kgl. Museum fur Naturkunde in 

 Berlin. 



Atax ahnormvpes was collected at Lake St. Clair during the 

 summer of 1893, but owing to confusion of different species 

 due to lack of familiarity with the group, no statement can be 

 made as to the hosts except that it was almost surely harbored 

 by Unio alatus, U. ventricosus and U. luteolus. It was next 

 met with at Grand Rapids, Mich., in the summer of 1895, 

 when individuals were found in U. ligamentinus, U. occidens, 

 U. ventricosus (very abundant), IT. alatus and IT. rectus from 

 different localities in Grand River, while collections made since 

 have added to the list of hosts IT. undulatus, and emphasized 

 the fact that it is far more abundant in IT. ventricosus than in 

 any other species of mussel. One specimen was found in that 

 species from Rogue River, Kent County, Mich., July 5, 1897. 

 It has been taken in limited numbers in IT. luteolus from 

 Reed's Lake near Grand Rapids, Mich., in the same Unio 

 from Long Lake, Kalamazoo, Mich. , and in that and IT. ventri- 



