Habits and structure of Cotylaspis insignis Lerpy. 205 
Shell No. of | Shell 
Shell | No. of 
No. of | Shell | No. of | 
in mm Cotylaspis in mm| Cotylaspis in mm) Cotylaspis lin mm Cotylaspis 
34 2 | 60 | 7 70 | 5 | 80 7 
1.608) 7 70 | 4 | 82 &) 
42 1 | 63 4 al 6 83 11 
45 4 63 7 | 73 2 ot | 6 
47 4 | 64 6 Werte 3 | 86 | 9 
47 6 | 66 | 4 73 4 | 89 10 
66 | 6 | 74 | 
51 2 66 | 14 A 4 | 
53 3 66 | 5 74 8 | 
56 6 66 3 1009 4 | 
57 3 6a 3 | 75 5 | 
58 6 68 1 |) mei 5 
59 4 68 | 1 ME 7 
68 | 3 77 13 
68 | 4 78 5 
69 | 1 79 4 | 
| 79 7 | 
| To) 9 | 
Total 11 42 | 16 76 | 18 | 97 GR 
Average Se | all 4.7 | 5.4 8.7 
These figures may be accepted as showing that, while the age 
of the host has some influence in accounting for the number of 
Cotylaspis present, it cannot be a determining factor, as is shown 
clearly by the fact that we find fourteen parasites in a host 66 mm 
long and only one in another 69 mm long. 
There are some noteworthy differences between the facts of 
distribution of Cotylaspis at Chautauqua Lake and in the localities 
that are noted by Keuter. He finds the parasite by no means 
restricted to Anodonta, but while it is not as generally found among 
the Unionidae as is Aspidogaster, still it is found in 24 of the 44 
different species of hosts that he examined, as against 37 hosts for 
Aspidogaster. He also finds that Cotylaspis is present in six of the 
ten localities that he examined, Aspidogaster being found in nine of 
them. In Lake Chautauqua, as noted, Cotylaspis is not found outside 
of the genus Anodonta (the exceptions being too occasional to be 
counted). As some of the localities studied by Kenuny are of the 
same river system as Lake Chautauqua and are nearer the mouth 
of the river, and as the occurrence of Cotylaspis, as well as of 
Aspidogaster, is more considerable in those places, the supposition is 
aroused that possibly the distribution of the parasite has been from 
the lower to the higher parts of the river system and that its 
absence from the other Unionidae in Chautauqua Lake means the 
shorter period since its introduction there. His figures indicate a 
