248 robert h. wolcott: 



The size of the mussel seems to have little effect. No 

 accurate records were made in regard to this fact previous to 

 the past summer and for reasons stated above, these records 

 are of little value in proving or disproving the fact of any 

 connection between size and percentage of mussels infested. 

 Generalizing from experience, in the absence of previous ac- 

 curately recorded observations, it seems, however, that there 

 is none. 



The same is true of sex, which seems to affect in no degree the 

 extent of parasitism, though it might be supposed that especially 

 in the case of a gravid female entrance by the mite might be 

 the more easily effected. 



Records kept the past summer also as to depths at which the 

 shell was buried and amount of vegetation on the bottom, 

 furnish no satisfactory data. It has become evident that it is 

 not an easy matter to collect facts in such form as to allow of 

 a proper comparison of the importance of the various factors 

 which determine the occurrence of parasitic mites in various 

 species of Unionidae and under different conditions. And it 

 has also become evident that perfectly accurate statements, 

 with the accumulation of the data necessary to furnish an 

 adequate basis for them, will only be possible after years of 

 careful observation. The author regrets that he has not the 

 benefit of such in the preparation of this paper, but hopes that 

 he may at some time in the not far distant future be able to 

 report more fully upon this exceedingly interesting subject of 

 research. 



The maximum number of mites found in a single shell has 

 occurred in the case of an Anodonta plana from a pool near 

 Lincoln, Neb., opened in September, 1895. In it were 15 Atax 

 ypsilophorus and 406 A. intermedins — 93 males and 313 

 females. The mussels collected in Nebraska, however, espec- 

 ially the Anodontas, have averaged more mites to the specimen 

 than those collected in Michigan, though the percentage of 

 those infested is about the same. 



The presence of these mites seems to entail few, if any, con- 

 sequences upon the host; though Garner (64) claims that their 



