OBSERVATIONS ON THE PARASITISM OF ANO- 



DONTA PLANA LEA BY A DISTOMID TREMA- 



TODE, AT CHAUTAUOUA, NEW YORK. 



HENRY LESLIE OSBORN. 



THE materials on which these observations are based were 

 collected at Chautauqua Assembly on the south shore of Lake 

 Chautauqua, New York, during the months of July and August 

 of 1895, 1896, and 1897. The animals are very abundant in 

 the semi-muddy bottoms near the shore, and can easily be seen 

 and watched in situ and reached and collected with the hand 

 from a boat. They are found in company with several species 

 of Unio, and it is not always possible to tell from the boat 

 whether one has found this genus or Unio. The studies were 

 made partly in the Biological Laboratory of the Chautauqua 

 College of Liberal Arts and partly at Hamline University, 

 Saint Paul, Minn. Most of these shells of Anodonta exhibit 

 on the inner surface a more or less extensive vermilion-yellow- 

 ochre coloration, in the form, apparently, of a foreign material 

 laid down at the expense of the nacre. This led me to study 

 the case carefully, and brought to light the fact that the red- 

 colored cases of Anodonta are infested by a distomid parasite 

 which lives in the space between the mantle and the shell, and 

 is apparently the agent chiefly concerned, directly or indirectly, 

 in the production of the red coloration. A somewhat careful 

 examination of the materials at hand has brought certain facts 

 to light which seem of interest as new or little known. 



The fact that shells of Anodonta are reddened has been 

 known since 1839, when Lea 1 was misled into describing shells 

 thus diseased from Ohio as a new species, Anodonta salmonea, 

 in language which so closely agrees with the case of the 

 Chautauqua shells as to leave no doubt of the identity of the 

 two. But so far as I have been able to ascertain, the colora- 



1 Lea, Trans. Am. Phil. Soc. N.S., vol. vi, p. 45. PI. XIV, Fig. 41. 1839. 



