04 Clark — Holoph yi ic Pl< i rikto n of Lakes Atitlan and Amatitlan . 



some writers to the species of this germs, I prefer to let it stand among 

 the forma already listed from the American continent. 



2. Microcystis marginata (Menegh.). 



Anacystis marginata Menegh., Nost., 03, Tab. XIII, fig. 4, 1841; Wolle, 



F. W. Alg. U. S., 320, 1887. 

 Microcystis marginata, Kuetzing, Tab. Phyc. I, (>, 1S4.V, Kirchner in Eng. 



and l'r., Nat. Pfl-fam. I, la, 56, 1900. 



In many of the samples (formalin material) collected in Lake Amatitlan, 

 the solid matter has separated, the heavier material settling to the bottom 

 and the lighter material coming to the top. The surface material is of a 

 bright hlue-green color, and is either coarsely floccvdent or exceedingly 

 fine in appearance. In case it is coarsely flocculent it is usually composed 

 mainly of Clathrocystis (q. v.) along with a few other elements such as 

 Microcystis, Anaba-na, Gomphosphieria and the like. "When it is exceed- 

 ingly fine in appearance it is found to be mainly Microcystis. 



In many cases it occurs in the vertical hauls, in which case it was pre- 

 sumably taken mainly in the upper part of the haul. A few colonies often 

 occur, however, in the bottom material. If any wasserbluethe occurs on 

 the Central American lakes it is probably mainly due to this Anabsena 

 and Clathrocystis. It occurs in large colonies (a colony of medium size 

 measures 1080m long and 400/* wide) composed of innumerable minute 

 bright blue-green cells 3-5/* in diameter. The families appeared to be 

 indistinctly arranged in minute looping strings, reminding one somewhat 

 of Clathrocystis, although no perforations in the colonies were evident. 



The identification of this form with M. marginata is not perfectly satis- 

 factory, inasmuch as the thin colorless tegument is not in evidence, and 

 the 'colonies are considerably too large. The latter matter, however, is 

 merely a matter of coherence, closely related to such local influences as 

 winds and calms. The tlialli quite closely resemble the figure of Micro- 

 hela firma (" Palmella firma Breb. & Lenorm") in Kuetzing's Tabulae 

 Phycologia. 



3. Clathrocystis robusta Clark sp. nov. 



Diagnosis: Thallus in younger stages a dense spherical colony of dark 

 blue-green spherical or oval cells, 0-9m in diameter, surrounded by a 

 spherical envelope of refractive jelly. Plant-body in later stages of growth 

 perforate, clathrate or broken up into elongate rounded lobes. Jelly 

 tardily deliquescent, finally wholly dissolving, leaving the plant-body a 

 densely cohering mass of cells. Colonies quite large and conspicuous. 

 Agrees in form and life history with Clathrocystis ivrngliiasa Kuetzing, 

 from which it differs in the much greater size of the individual cells. 

 Color in formalin bright blue. Type material Sample No. 1, collected 

 at bake Amatitlan, Guatemala, February 1, 1906, by Dr. Seth E. Meek. 



The type material will be deposited in the l T . S. Museum. 



This alga is abundant in the surface material of the collections from 

 Lake Amatitlan, forming a flocculent bright blue-green scum. It is at 



