these were supplemented by one or more additional counts when the agree- 

 ment was not close. 



In 1928, only the adult Crustacea of the plankton were 

 counted, and no record was made of the nauplii and rotifers. In 1929 

 nauplii, but not rotifers, were counted; and in 1930 both were counted. 

 The more complete counts of 1930 were made possible by combining many 

 of the series in one sample for each station. 



Data and discussion 

 Qualitative Data 



The rotifers were not studied to determine the species present. 

 In 1929, the plankton Crustacea were identified by Dr. Stillman Wright; 

 in 1930, this was done by the late C. Dwight Marsh, and the identifications 

 of cladocera were checked by Dr. J, P. Visscher, Western Reserve University. 

 Rather than present a complete list, only the more important species are 

 mentioned in the following summary, which was taken almost without change 

 from a report prepared by Dr. Marsh, 



The crutacean fauna of Western Lake Erie is, in many respects, 

 intermediate in character between that of the deeper Great Lakes and 

 smaller bodies of water. Of the species of Diaptomus in the deeper 

 Great Lakes, the common forms are D. sicilis , D. minutus, and D, ashlandi ; 

 D. oregonensis is present, but is not common. In Western Lake Erie 

 D. oregonensis is the prevailing form of this genus; D. sicilis , D, 

 minutus , and D. ashlandi are found, but are not in great numbers. 

 D. siciloides is not reported from the other Great Lakes, but is fairly 

 common in pools and small lakes; apparently in Lake Erie it is not character- 

 istic but occurs because of the connection of Lake Erie with small bodies 

 of water. Its appearance in the lake seems to be accidental. 



The plankton all over the area examined is quite uniform in its 

 characteristics. The only difference is that in localities near shores 

 there may be sporadic introduction of species from potamoplankton or 

 heleoplankton, as for example Diaptomus siciloides and a number of the 

 Cladocera. This does not mean a quantitative uniformity, however, 



Cyclops americanus and C_^ Brevispinosus are found in Western 

 Lake Erie in considerable numbers. Generally speaking C, americanus 

 is characteristic of small bodies of water; C, brevispinosus is most 

 frequently limnetic in habitat. 



The characteristic Cladocera are the retrocurva form of Daphnia 

 pulex parapulex , Leptodora kindtii, Diaphanosoma leuchtenbergianum , and 



208 



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