April, 1908. Lake Amatitlan and Atitlan — Meek. 197 



onies are said to attain a diameter of 40-100 ,u., and individual 



cells as much as 25 11. 



Eudorina stagnate Wolle. 



This is one of the common elements of the plankton, occurring 

 in the greater number of samples, never in great abundance, but 

 usually several, and often numerous examples could be seen in the 

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

 of active division. 



I have not had opportunity to compare carefully Wolle's 

 description of Eudorina stagnale with the description of the 

 European form, elegans Schmidle. In a recent article on Algae 

 from Brazil, he identifies the Eudorina found there as elegans. 



Family Perltliiildie. 



Peridinium tabulatum Ehrenberg. 



Common in most of the plankton, abundant in a good deal of it. 

 The form at hand is that with the cleft anterior portion ; diameter 

 of a specimen measured, 65 /i. Griffith and Henfrey give the 

 length as 1-480", which reduces to 5 2 /^. All our examples appear 

 to be of nearly uniform size. They are exceedingly 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 remarkable 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. 



Peridinium hirundinella O. F. Muller. 



Rather common; scattered through most of the phyto- 

 plankton from Lake Amatitlan, and also in the Atitlan material. 

 Our specimens agree very well with the figures found in Kent, 

 and in the figures in the Riverside Natural History. All are 

 robust and quite rough. 



This species is almost cosmopolitan, having been reported 

 • from England, India (Kent), the Great Lakes (Riverside Nat. 

 Hist.), and from lakes in Iceland (Ostenfold). (I have so far 

 found none in Lake McDonald, Alaska, though there are several 

 other species represented.) Apstein (1, c.) notes slender 3 -homed 

 specimens as occurring in the Dorbesdorfer Sea. All the exam- 



