236 kobert h. wolcott: 



footiana; from Plaster Creek in A. ovata; and from the mill 

 pond at Mill Creek in A. plana and U. pressus. 



At White Lake, Muskegon County, Mich., it was collected 

 during the past season in A. subgibbosa, A. subcylindacea, A. 

 footiana and M. complanata. 



In Illinois, it has been found in A. corpulenta and A. imbe- 

 cilis from the Illinois river at Havana and in A. suborbiculata 

 from Thompson's Lake near Havana. In Iowa it has been 

 obtained in the Cedar River from M. rugosa at Mt. Yernon. 

 In Nebraska the writer has collected it in U. subrostratus and 

 A. grand/is from pools near Lincoln; in M. complanata, A. 

 plana and A. decora from Weeping Water Creek, Weeping 

 Water; and in A. grandis, A. plana and M. complanata from 

 the Blue River at Milford. 



From the material received from Chautauqua Lake, N. Y., 

 it is apparently as common as in all other localities cited, and 

 has been collected in A. plana and A. edentula. 



The record of collections shows that it is essentially an Ano- 

 donta parasite, though occuring in Mavgaritana and rarely in 

 Unio. 



12. ATAX TUMIDUS WOLCOTT. 



At ax tumidus Wolcott, 98; 285. 



Very similar to A. (N.) iwgens in form and in size, the females of both 

 showing a tendency to enormous distension when filled with eggs, in the 

 relative length of the legs, and also in color, the internal structure of each 

 as a rule giving no suggestion of the usual Y-shaped mark, but the color be- 

 ing a light brown with numerous fine white vermiculate lines, though speci- 

 mens of A. tumidus have been found showing quite a well defined Y-mark. 

 It was stated in the preliminary description of the species that it also 

 agreed in the manner of depositing eggs, but the possibility of an error 

 in this statement was changed to a probability by careful observations on 

 this point during the past summer. 



The species is, under normal conditions, one of the largest of the 

 genus, the females measuring from 1.4 to 1.5 mm. in length and when 

 filled with eggs even 1.8 or 2.0 mm., the males ranging from 1.10 to 1.25 

 mm. The body is oval, broadened posteriorly, evenly rounded at both 

 ends and uniformly arched, being also highest posteriorly. 



Eyes small, black, and separated from each other by a considerable 

 distance. 



Maxillary shield similar to that of A. (N.) ingens, short and broad, 

 with no ancoral process produced posteriorly, and with muscles attached 

 to long curved processes projecting from the sides backward and upward. 



