NORTH AMERICAN SPECIES OF THE GENUS ATAX 201 



Mr. M. Kicker of Burlington, Iowa, has kindly sent a small 

 collection of mites obtained at Havana, Ills., from the same 

 species of Unionidae enumerated in the above list. 



The present paper embodies, thus, the results of the exami- 

 nation of nearly 3,500 mussels, representing 60 species, and 

 from them have been collected and preserved about 7,000 

 mites, belonging to 13 species, of which 7 are new and 3 more 

 are reported from America for the first time. Search has been 

 made for mites in Pisidium and Sphcerium but with success in 

 only one instance, when two individuals of A. crassipes (Muller) 

 were found in a species of Sphoerium, and in Cam/peloma, 

 Physa, Limnea and Goniobasis, but so far without results. 



In this enumeration and throughout the paper the author has 

 avoided any attempt to pass judgment upon the validity of the 

 different species of mussels referred to, and has included many 

 names which he himself believes to be synonyms, as for 

 instance, Unio occidens Lea and O. ventricosus Barnes, in order 

 that there should be in this way no omissions of species which 

 others might believe distinct from those given. All the 

 names given have been more or less generally recognized and 

 the reader is requested to make his own synonymical corrections 

 in accordance with his opinions. 



The specimens of mites obtained were studied alive, pre- 

 served in various fluids, and mounted upon slides to allow of 

 thorough microscopical examination. Without, at first, suf- 

 ficient knowledge of the weight of specific characters, too much 

 dependence was placed upon color, which, it is found, has 

 almost no value in identification, though the brilliancy of 

 coloration is one of the principal features which make the group 

 such an exceedingly attractive one for study. Later certain 

 structural characters were fixed upon, which, by their similarity 

 in allied species, led to confusion; and differences, too, which 

 were at first assumed to be sexual, were found later, when the 

 true sexual characters were discovered, to be specific. Finally, 

 especially at first, the mites collected from a single species of 

 mussel and bearing a close resemblance were assumed to be 

 identical and only found to include more than one species after 



