230 bobert h. wolcott: 



measurements of a male: 



Length of body 0.835 mm. 



Length of leg 1 0.811mm. 



Length of leg K 0.995 mm. 



Length of leg III 1.107 mm. 



Length of leg IV 1.250 mm. 



No female is in such a condition on the slide as to allow of ready or 

 accurate measurement. 



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

 Museum of Comparative Zoology of Harvard University, in the United 

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

 Berlin. 



This species when collected was considered to be the male of 

 A. fossulatus, but when slide-mounts of that species were made 

 the true male was discovered, and also both sexes of the 

 present form. The most striking difference, and that first 

 noted, was in the position of the acetabula in one line, hence 

 the name "striata," but careful observation showed the 

 presence of other differences as above indicated and also that 

 these differences, though slight, were constant. It may be a 

 variety of A. fossulatus, but it is for the present considered 

 separate, though closely allied. 



Specimens were taken at Grand Rapids, Mich., during the 

 summer of 1895, among A. fossulatus, from JJ. coccineus, JJ. 

 ligamentinus, JJ. occidens, JJ. rectus, TJ.rubiginosus, JJ. School- 

 crafti, JJ. undadatus, JJ. verrucosus and JJ. alatus — 89 speci- 

 mens altogether — but owing to their being confused with A. 

 fossulatus no statement can be made as to the exact source. 

 Collections of many more of the same mussels from near the 

 same localities, this last summer, it was hoped would give more 

 definite information, but only one specimen was found, which 

 was in JJ. undid atus. 



In Nebraska it has been collected from JJ. Jamesianus and 

 JJ. lachrymosus from pools near Lincoln, from JJ. undulatus, 

 JJ. lachrymosus, JJ. rubiginosus and JJ. Jamesianus at Weeping 

 Water, from Weeping Water Creek; and from JJ. lachrymosus 

 from the Blue River at Milford. The Nebraska specimens are 

 all peculiar in that the genital area is a little smaller and the 



