shown that this cladoceran was present in large abun- 

 dance in the bottom mud of the eastern end of the 

 lake during the latter part of June. This would sug- 

 gest that during the breeding season Leptodora fre- 

 quents the bottom and either stays in the mud or so 

 close to it that the bottom meter net, which was 

 elevated a little above the mud, caught only a few 

 stragglers. 



Mysis was taken at 14 stations, always in the 

 bottom net but not always in the deepest water, al- 

 though that is its usual haunt. It was found along 

 both the Canadian and American shores in the east- 

 ern portion of the lake, and near Lorain on the Amer- 

 ican shore in the western portion. The 3 highest per- 

 centages were east of Long Point in water from 40 

 to 60 meters in depth and a little nearer the Canadian 

 shore. The genus Pontoporeia was collected in the 

 bottom net at 3 of the deepest stations in the eastern 

 end of the lake. 



July Distribution 



The total bulk of the samples increased to 3 1/2 

 times that of June, and this increase was largely due 

 to cladocerans. As a result, although the actual 

 numbers of the copepods also increased, their per- 

 centages showed a considerable decrease, especially 

 in the shallower portions of the lake (fig. 60). The 

 only stations at which the copepods still surpassed the 

 cladocerans were in the deepest portion of the lake 

 at the eastern end near the Canadian shore. 



Cyclops were again distributed over the entire 

 lake but their percentages were even smaller than in 

 June. Cyclo ps l euckart i was taken either in the sur- 

 face or in the bottom net at every station, but in 26 

 of the tows it constituted a mere trace, and only 

 once did its percentage rise above 3. It was slightly 

 more abundant in the western portion of the lake, 

 while C. bicuspidatus predominated in the eastern 

 portion. 



Diaptomus retained its numerical superiority 

 over the other copepods only in the western part of 

 the lake; in the eastern part it was outnumbered by 

 Eplschura and in the central part by Li mnoca lanus. 

 There were 2 species of the genus, as during June, 

 but now their relative abundance was reversed, and 

 p. ashla ndi had become more numerous thanD. 

 sicilis in the western end of the lake and in the deep 

 water at the eastern end. This reversal, however, 



was due as much to a marked decrease in the num- 

 bers of the latter species as to any increase in the 

 numbers of the former species. 



Episc hura decreased in abundance but its distri- 

 bution increased so that during this month it was 

 found at every station and with but 3 exceptions in 

 both surface and bottom samples. Although the high- 

 est percentages were still at the surface, it was much 

 more equally divided. It was more numerous along 

 the American shore for the entire length of the lake. 

 The eastern half of the lake maintained its superiority 

 over the western half both in actual numbers and in 

 percentages. 



Limnocalanus, which was found at nearly every 

 station in June, was practically confined to the deep- 

 er portions of the lake during July. It was absent 

 from 13 stations in the shallower waters and consti- 

 tuted but a trace at 5 others. At the deepest station 

 in the lake it still had a percentage of 74 in the bot- 

 tom net and 23 at the surface, and these figures com- 

 bined with those of the other copepods at this station 

 left the cladocerans in a very small minority. This 

 suggests that while Limnocalanus is widely distributed 

 during the colder portion of the year, when summer 

 temperatures are reached there is an active migration 

 from the surface toward the bottom, and from the 

 shallower to the deeper portions of the lake. 



Dap hnia was found at the surface and at the bot- 

 tom in every tow taken during July, and its percent- 

 ages had so increased that at 27 stations it consti- 

 tuted more than half of the catch. It had also be- 

 come fully as abundant in the eastern as in the west- 

 ern part of the lake, but showed a rather marked 

 diminution in the central portion. The combined 

 varieties of D. longispina were more numerous at 

 the eastern end of the lake while D. pulex was more 

 numerous at the western end. This is another bit of 

 evidence which suggests that the latter species breeds 

 in Sandusky Bay. 



Holope dium was scattered sparingly throughout 

 the entire lake, but its numbers were so small as to 

 constitute a mere trace in all but 2 of the tows. 

 Moreover, it was absent from more than half the bot- 

 tom catches and from all the surface samples except 

 2 in the middle of the lake. On the other hand, Sida 



had spread over the entire lake and appeared in every 

 tow, and usually in both surface and bottom samples. 

 The percentages also greatly increased and in the 



157 



