Clark — Holoph ytic Plan Hon of Lakes Atitlan and Amatitlan . 93 



algae, entomostraca are quite abundant. Among the holozoic 

 forms, in addition to entomostraca, a rotifer, resembling Anureea 

 cochlearis, is quite abundant, and another, probably Notholca 

 longispina, very common. 



One of the most striking features of Lake Amatitlan, and 

 perhaps of tropical lakes in general is the indication of " wasser- 

 bluethe* " during February, and therefore probably throughout 

 the year. Although the field notes do not make special men- 

 tion of " wasserbluethe," the presence of Clathrocystis and Ana- 

 basna, both characteristic wasserbluethe plants, together with 

 the notes " abundant on surface," make it almost certain that 

 wasserbluethe is present. This would indicate, also, that 

 probably the same elements of plankton are present and in 

 pretty uniform quantities the year round, so that plankton- 

 taking for a few weeks would be a fair gauge of what was really 

 in the lake at any time. In more northern lakes, or in cooler 

 regions, with extreme seasons, a short series of hauls during a 

 single season would mean almost nothing. 



The following is a list of the alga? represented in the collection : 



Order COCOGONyE. 

 1. Gloeocystis rupestris (Lyngb.). 



Palmetto, rupestris Lyngb., Hydro. Dan., 207, pi. 69, 1819. 



Glcecapsa polydermatica Kuetzing, Tab. Phyc, I, 15, Tab. 20, fig. Ill, 



1845; Wolle, F. W. Alg. U. S., 331, pi. CCX, figs. 29-31, 1887. 



Gloeocystis is very rare in the collection ; only one example was noted, 

 this was in a sample of plankton collected from the surface of Atitlan in 

 front of the hotel, February 18, 9 p. M. 



It may be remarked that some authors, Wolle in particular, regard 

 this genus as simply the early condition of some higher alga, and place 

 no value on specific distinctions between the various forms. The example 

 seen agrees very well with Wolle' s figures and brief description. Com- 

 pared with Kuetzing' s plates it more closely resembles his quaternata 

 than any other but in view of the very little significance attached by 



* The term " wasserbluethe " is here used to indicate the minute algpe, mostly blue- 

 greens, which come to the surface and form a scum. In this strict sense there was no 

 " wasserbluethe " present. The expression " abundant on the surface," put on many of 

 the labels by me, should have been, " abundant at or near the surface," for nearly all of 

 the alga? so evident to the naked eye were distributed in the stratum of water from the 

 surface to the depth of a meter or more. . Where it was driven in masses, apparently by 

 the wind, it nowhere formed a scum on the surface even when the water had been but 

 little if any agitated by the wind for one or more days. " Wasserbluethe " could not be 

 said to exist in the lower half of tin- lake. The presence of so much Anabxna flos-aquie 

 near the surface in the upper half of the lake certainly indicated that " wasserbluethe " 

 did exist there at least to a limited extent (Meek). 



