70 MICHIGAN SURVEY, 1908. 



The temperatures observed on July 11 may be given as an example. 



The absence of plant growth also tends to limit the number and char- 

 acter of species to predatory forms, and the number of individuals is 

 small. 



A small rock beach jutted into the lake near the light-house, and 

 was at most but one meter high. Although sheltered from the waves 

 by an island, it was still completely flooded by even moderate waves. 

 Most of the surface was accordingly without vegetation, but besides 

 the crustaceous lichens there was one species of moss, a few plants 

 of harebell, and several tufts of grass. Five species of insects were found 

 on this beach, four of which were merely casual visitors. Some spiders 

 (No. 46), Pardosa groenlandica Thor., wandered upon the rock from the 

 neighboring gravel beach, but finding no rocks to hide under they soon 

 left. Ants (No. 46), Formica dry as Wheeler, were rather common, but 

 it was easy to see that they came from, and returned to, the gravel 

 beach. The only food they obtained appeared to be the remains of dead 

 caddice flies. A species of fly, Hydrophorus philomirius Wheeler (No. 

 46), was very common on those parts of the rock which were constantly 

 wet by the waves. They were seldom seen over the dry. portions, but re- 

 mained resting on the wet rocks. This fly was of common occurrence 

 in the uplands and will be mentioned also under other headings. A 

 few stoneflies (No. 46) were found on the wet rocks where the waves 

 ' struck. The only species confined to the beach was one species of beetle, 

 Bembidiv/in grapei, which ran over the surface, hiding from time to time 

 in tufts of moss. 



On a smaller rock beach exposed to the full force of the waves wero' 

 collected a spider (No. 47) and an ant, Formwa dryas Wheeler (No. 

 47) ; a butterfly (No. il) , Basilarchia arthemis Dru., was also taken, while 

 hovering over the beach. 



On a larger beach near by, the elevations of which were given in a 

 preceding paragraph, the faufta was better developed. A jumping spider 

 was fairly abundant, and was a fine example of protective coloration,, 

 being almost invisible against the gi'ay rock background. Another spider 

 (No. 48) and red mites (No. 48) hid under the foliaceous lichens. A small 

 beetle (No. 48) was abundant, running rapidly over the rock, never- 

 attempting to fly, but hiding in the crevices. A brightly colored red 

 and black beetle was common. It ran rather slowly but flew easily. No 

 ants were seen. Besides the forms just mentioned, which may be con- 

 sidered normal members of the rock beach association, there was collected 

 a caddice fly (No. 48) and a running spider (No. 48), undoubtedly a 

 straggler from the Cladonia zone above. 



