304 OS BORN. [VOL. I. 



always an anterior strip in both valves if there is in one, and 

 so on. In some cases the amount of the red color is so great 

 that the shell lining is thrown into folds ; in such a case we 

 find folds on both sides, but they are not symmetrical, and in 

 this minor point the symmetry is slightly lost. 



It will be interesting to inquire whether the amount of the 

 coloration is correlated with the age of the host. I suppose 

 that we are justified in using the size of the shell as a criterion 

 of the age of the animal, and if so, then we must conclude 

 that the amount of the coloration is not in any way correlated 

 with the age of the shell. It would be possible to find all 

 sizes of shells with every stage of amount of color, - - small 

 ones in which there was little and much, and largest ones in 

 which there was much. I have tabulated here a few measure- 

 ments and amounts of coloration : 



EXTREME LENGTH OF VALVE. 

 mm. mm. mm. mm. mm. 



So 



I am not able to state the percentage of Anodontas in which 

 the red coloration is found ; it is very prevalent, but not 

 universal. Speaking very roughly, I should give it as my 

 belief that at least 75 per cent of the animals at Chautauqua 

 are affected, and I feel tempted to put the estimate even 

 higher, for it is not at all frequently that one runs across a 

 specimen in which the shell is absolutely normal. 



It is an interesting and striking fact that the presence of 

 the parasites is practically confined to the Anodontas. There 

 are several species of Unio found in company with Anodonta, 

 and these have all of them been carefully examined for the 

 fluke. A single case of it has indeed been found, 1 --a speci- 

 men of Unio edcntula, in which the shell exhibited the red 

 coloration and flukes were found which seemed to be identical 

 with those so commonly found in Anodonta plana. This case 



1 By Mr. R. H. Johnson. 



