Clark — Holophytic Plankton of Lakes Atitlan and Amatitlan. 103 



vary greatly in size, some filaments being 25m in diameter with the cells 

 80m long, while others are only 10m in diameter. The peculiar arrange- 

 ment of the chlorophyl as described in the diagnosis above may represent 

 the formation of gonidia, but the smaller plants have this arrangement 

 as well as the old. It is probable that the plant is reproducing, and that 

 the gametes or gonidia have recently escaped from the ends of the larger 

 filaments, the peripheral walls of which project considerably beyond the 

 terminal septa? in many instances. 



"West's notes on the genus Tribonema, a generic name which lias been 

 proposed for Conferva which some authors do not regard as having been 

 sufficiently defined (Brit. F. W. Alg. 256) fit in well with this species and 

 appear to point out pretty clearly where it should belong. The chromato- 

 phores are parietal, "Asexual reproduction takes place by globular or 

 ellipsoidal aplanospores and it is related to Ophiocytium." In its habit of 

 curling in the fashion of a corkscrew it bears a strong superficial resem- 

 blance to Ophiocytium, but can be distinguished from the species of that 

 genus at once by the numerous septa? and truncate ends. The peculiar 

 spiral growth, however, is possibly merely physiological, and may be, as 

 Ostenfeld has pointed out in the case of a much curved form of Melosira 

 granulata noted in one of the lakes of Iceland (Journ. de Botanique, Bot. 

 Tids. Kjobenhaven, XXVI, fasc. 22, p. 2.33), "an interesting adaptation 

 to the limnetic condition . ' ' 



Order (EDOGONIACE.E . 

 27. liulbocliate sp. 



A few sterile plants of Bulbochsete were found mixed in with the Glozo- 

 trichia, but on account of their sterile condition, I could not identify them 

 with any degree of certainty. The following notes were made: 



Cells rather short and stout, somewhat turgid, the diameter from 15 to 

 18m, the length from 25 to 28m; each living cell contains a bright, large 

 eye-spot, and a number of cells are empty. Filament rather well branched ; 

 lateral set* short with a small bulb ; terminal setre long and slender, occa- 

 sionally terminating in a clavate expansion. 



The following is a list of the holophytic species occurring in the Zoo- 

 plankton. Besides these, rotifers and entomostracans were present in 

 considerable numbers. 



Order FLAGELLATA. 

 1. Coelastrum microporum Xaegeli. 

 Ccelastrum microporum Na?geli (Ref. not found) Wolle, F. W. Alg. U. S. 

 171, 1887. 



Not uncommon, a few specimens found scattered through samples No. 

 19 (February 5, Amatitlan, towing made at noon from bottom to top in 

 110 feet of water) and No. 20 (Lake Amatitlan in front of hotel, Jan- 



