104 Clark — Holophytie Plankton of Lakes Atitlan and Amatitlan. 



uary 17). None of these specimens showed the tubercles on the cells 

 shown in many illustrations, but according to descriptions and a few 

 figures, these may he absent. One colony appeared to possess eye-spots, 

 one in each cell. One colony examined measured 60> diameter, cells 15m. 

 Full grown colonies are said to attain a diameter of 40-100^, and indi- 

 vidual cells as much as 25/*- 



2. Eudorina stagnale AVolle. 



Eudorina stagnale Wolle, F. W. Alg, U. S., 160, pi. CLII, figs. 11-21, 

 1887. 



This is one of the common elements of the plankton. It occurred in the 

 greater number of samples, never in great abundance, but usually several 

 and often numerous examples could be seen in the field of the microscope 

 at the same time. It was quite frequently found in stages of active 

 division. 



There is probably little if any difference between this and the European 

 form elegans. Schmidle, in a recent article on Alga? from Brazil 

 (Hedwigia, Vol. 40, 46), identifies the Eudorina found there as elegans. 



Order DINOFLAGELLATA. 



3. Peridinium tabulatum (Ehrenberg). 



Glenodinium tabulatum Ehrenberg, Inf. 257, Taf. XXII, fig. XXIII, 



1838. 

 Peridinium tabulatum, Kent, Man. Inf., I, 448, III, pi. XXV, figs. 1-5 



and 55-57, 1880-1882; Griffith and Ilenf., Mic. Diet., 1883; Apstein, 



Sussw-p., 152, fig. 52, 1896. 



Common or abundant in most of (he plankton. The form at hand is 

 that with the cleft anterior portion; diameter of a specimen measured, 

 63/*. Griffith and Ilenfrey give the length as 1-480" which reduces to 52m. 



All our examples appear to be of nearly uniform size. They are exceed- 

 ingly abundant in sample 8, collected at the west end of Lake Amatitlan 

 on the surface. This catch consisted mostly of insect exuviae and it is 

 worthy of remark that the greater number of the Peridiniums were 

 crowded densely in the cast-off skins as if they had worked their way in 

 for food or shelter. 



4. Ceratium hirundinella (O. F. Midler). 



Bursaria hirundinella O. F. Muller, Yermiuni terrest. , I, 63, 1773. 



< 'indium lonrjicorne (Perty) Kent. Man. Inf., I, 457, III, pi. XXV, fig. 



26, 1880-1881. 

 "Ceratium macroceras Shrank " Kef. not found. 

 Ceratium hirundinella, Apstein. Sussw-p., 149, tigs. 48-50, 1896. 



Rather common, scattered through most of the phytoplankton from 

 Lake Amatitlan, and also in the Atitlan material. Our specimens agree 



