NORTH AMERICAN SPECIES OF THE GENUS ATAX 197 



pected from the number of years that have elapsed, the nature 

 of the specimens, and the crudity of methods of preservation 

 in. vogue at the time they were described. 



Thos. Say, in 1821, described Jlydrachna triangularis from 

 Unio cariosus Say; in so doing he may have re-described Atax 

 ypsilophorus (Bonz) as other authors have inferred, although 

 from his description it is impossible to say which species he 

 had under observation. In 1836, James D. Dana and James 

 Whelpley, in Silliman's Journal, described two forms, Hy- 

 drachna formosa from u Anodonta cataracta" (A. fluviatilis 

 Dillw.) and " Unio purpurata" (an incorrect identification as 

 TJ. pwpuratus Lam. is Southern in its habitat) ; and Hydrachna 

 pyriformis from Margaritana undulata Say. The former is 

 another synonym of A. ypsilophorus (Bonz), the latter a dis- 

 tinct species, but the characters given are not sufficient for 

 exact determination. Its form and the character of the claws 

 which are described as simple, seem to show that it is a female 

 of either A. abnormipes mihi or A. indistinctus mihi, but of 

 which it is impossible to tell. In 1812, S. S. Haldeman 

 described under the "Genus? Unionicola''' 1 nine species: 

 oviformis, lactea, personata, humerosa, symmetrica, proxima, 

 lugubris, unicolor and reticulata — with very short descrip- 

 tions, based mostly on color. Two of the nine are identi- 

 cal with A. ypsilophorus (Bonz), while the other seven are 

 probably the same, as Koenike (95b) suggests. Joseph 

 Leidy, in 1883, noted the presence of the same European 

 form in Anodonta fluviatilis Dillw. from New Jersey, and 

 mentions the occurrence in Unio complanatus Sol. of a second 

 species, "probably", he says, "1. BonzV\ also a previously 

 described European form. In 1891, F. Koenike of Bremen, 

 Germany, published a preliminary account (91c) of some 

 material received from Dr. Tyrrell in Ottawa, Canada, con- 

 firming Leidy' s observation as to the occurrence of A. ypsil- 

 ophorus (Bonz) in North America, but, and it seems rightly, 

 throwing doubt on his identification of A. Bonzi Claparede. In 

 1895, a fuller paper (95b) on the same material by the same 

 author appeared and in it he enumerated the species previously 



