Clark — Holophytic Plankton of Lakes Atitlan and Amatitlan . 1 05 



very well with the figures in Kent, and those in the Riverside Natural 

 History. All are robust and quite rough. 



This species is almost cosmopolitan, having been reported from Eng- 

 land, India (Kent), the Great Lakes (Riverside Nat. Hist.), and from 

 lakes in Iceland. (I have so far found none in material examined 

 from Lake McDonald, Alaska, though there are several other species 

 represented.) Apstein (1. c. ), notes slender 3-horned specimens as occur- 

 ring in the Dorbersdorf Lakes. All the examples seen from Lake Atitlan 

 are 4-horned but many, perhaps the majority, from Lake Amatitlan, are 

 3-horned. They do not appear to be more slender than the others how- 

 ever. Kent gives the sizes as ' ' length 1-120" to 1-90" 208/^-277/*. ' ' The 

 examples at hand measure 220m long and 70/* wide at the broadest portion 

 of the body. 



