NORTH AMERICAN SPECIES OF THE GENUS ATAX 235 



opening outward toward the acetabula, but not reaching them. The two 

 plates in the male bear a few small spines and the margins next the 

 groove are not thickened or produced. But in the female, these margins 

 are thick, and produced outwardly in front of the genital opening to 

 form two wide lips, which diverge at their tips. These lips each bear 

 along their margins several spines, a small one anteriorly and two or 

 three longer, stouter and somewhat cuiwed ones about the middle. Be- 

 hind the genital opening the lips are not so prominent and there is but a 

 single longer and more slender spine. 



MEASUREMENTS OF A FEMALE: 



Female 



Length of body 1.336 mm. 



Length of leg 1 1.030 mm. 



Length of leg II 1.515 mm. 



Length of leg III 1.326 mm. 



Length of leg IV 2.147 mm. 



Palpus 0.495 mm. 



The number of previous records of the occurrence of this 

 species in North America is such as to show it a very common and 

 widely distributed form. Dana and Whelpley (36) found it at 

 New Haven, Ct., in A. Huviatilis Dillw, and in a second species 

 of mussel which they incorrectly identified as Unio purpuraius 

 Lam. Haldeman (42j seems to have collected it in A. fluvia- 

 tilis, U. radiatus and U. cariosus from the Susquehanna River, 

 Pa. Leidy (83) records it in A. jluviatilis from Clarksboro, 

 N. J., and Koenike (95b) from Canada, in Anodonta frag His. 



It was found to be common in the summer of 1893 at Lake 

 St. Clair, in A. ovata, and also at Lansing, Mich., in the fall 

 of the same year though in what mussels is uncertain. 



In Northern Michigan it was equally abundant the next 

 summer, being collected in A. subcyUndracea and A. fooUcma 

 from Round Lake at Charlevoix; from the same and also 

 from A. edentula and A. fragllis, from u 26 " and Twin 

 Lakes in the vicinity of Charlevoix ; and in A. suhcyh'ndracea 

 and A. fragiUs from Intermediate Lake at Ellsworth, Mich. 



At Grand Rapids, Mich., it is abundant and has been col- 

 lected in numerous localities along Grand River, in U. press us, 

 M. marginuta, 31. rugosa, A. edenttda, A. ovata, A. sybeylm- 

 dracea and A. footiana; from Reed's Lake in A. j 'rag ill 's\ from 

 Rogue River, Kent County, in M. rugosa, A. ovata and A. 



