surface samples they often comprised more than half 

 the entire catch. At station 40 in the western-cen- 

 tral portion of the lake they made up 94 percent of 

 the plankton. 



L eptodora also extended its distribution and ap- 

 peared at every station except 4 in the Deep Hole 

 off Long Point. It showed larger percentages at the 

 bottom than at the surface, and was more abundant 

 at the western end of the lake than at the eastern 

 end. These records, however, were from meter net 

 hauls; the Helgoland trawl was not used during 1929; 

 if it had been, perhaps it would have shown as great 

 a preponderance at the eastern end of the lake as 

 during 1928. 



Mysis and Pontoporeia were more restricted in 

 distribution during this month, and were strictly con- 

 fined to the bottom in the deepest part of the lake. 

 The former genus appeared at 3 stations, but the lat- 

 ter at only the deepest station. No. 15. 



August Distribution 



The total bulk of the samples diminished slight- 

 ly , but still remained at least 3 times as great as in 

 June. As in July the large totals were due to in- 

 creases among the cladocerans rather than among the 

 copepods, and the former outnumbered the latter 

 everywhere except at 4 stations (fig. 61). 



Cyclops bicuspidatus and^. ro bust us practically 

 disappeared, the former being found at only 4 stations 

 and the latter at a single station in very small num- 

 bers. Cyclops leuckarti became more widely dis- 

 tributed than in June and July, and its percentages be- 

 came slightly larger. It was more common at the 

 surface and was present at nearly every station, but 

 was absent from more than half the bottom tows. 



Two Diaptomu s species were taken at practical- 

 ly every station, the percentages being slightly larg- 

 er in the western portion of the lake as well as at the 

 surface. During August a third species, D. minutus, 

 appeared in very small numbers at 4 of the littoral 

 stations in the bottom net. This was its only appear- 

 ance outside of the marginal zone during the entire 

 survey; only 1 or 2 specimens were found at each of 

 the 4 stations. It seems inconsistent that this, the 

 smallest of the Diaptomus species, should come out 

 of the marginal zone into deeper water, and that the 

 much larger species, D. oregonensis , was not cap- 

 tured outside the marginal zone once during the en- 

 tire survey. ^59 



Epischura had about the same distribution as in 

 July and was quite evenly divided between the sur- 

 face and bottom samples, but its percentages dimin- 

 ished considerably. Although it was present at every 

 station tliroughout the entire lake, it was still some- 

 what more abundant on the American than on the 

 Canadian side. Its highest percentage during the 

 month was at the extreme western end of the lake. 



Limnocalanus was again confined to the stations 

 in the deeper portions of the lake with the exception 

 of 4 in the littoral zone rather close to the shore. 

 Two of these were on the Canadian side, off Rondeau 

 Harbor and near Point Pelee; the other two were on 

 the American side, off Cleveland and Lorain, Ohio. 

 In the bottom samples at the deepest stations, the 

 percentage of this copepod still remained above 50, 

 and thus furnished another evidence of migration 

 from the shallower waters into the cool layer below 

 the thermocline. 



The Daphnla species showed further increases 

 and during August surpassed all the other macro - 

 plankton except at 1 or 2 stations. The numbers of 

 D. pul ex were greater than those of the combined 

 varieties of D. longispina, especially in the bottom 

 samples. And yet the highest percentage (100) of 

 D. pulex was found in a surface net haul at one of the 

 stations in the Uttoral zone near the Canadian shore 

 at the western end of the lake. The general distri- 

 bution of the 2 species was fairly equal throughout the 

 entire lake and no section showed appreciable pre- 

 ponderance. 



Holopedium disappeared entirely during this 

 month and its place was taken by another cladoceran, 

 Diaphanosoma leucht enber gianum. This species was 

 confined to the central and western portions of the 

 lake and did not appear at all east of Long Point. 

 This fact will account for its absence from the tows 

 taken during 1928 since they were made in the east- 

 ern end of the lake. Sida remained as widely dis- 

 tributed as in July and its numbers were nearly as 

 large, but it showed for the first time a decided dif- 

 ference in vertical distribution; the surface samples 

 contained practically all the larger percentages. 



Leptodora increased its distribution so that during 

 August it was present at every station in the lake and 

 usually occurred in both the surface and bottom nets. 

 Its percentages increased even more than its distri- 

 bution and at 2 stations at the western end of the 

 lake on the American side it formed one -third of the 



