236 FRESH-WATER BIOLOGY 



174 (173) Spicules siliceous, in the form of plates and delicate radiating 



spines Acanthocystis Carter. 



Representative species. . . Acanthocystis chaetophora Leidy 1874. 



The skeletal plates are oval, arranged tangentially. The 

 spinous rays are of two lengths, the long ones acutely forked, 

 the short ones widely forked at the distal extremities. Nucleus 

 large, usually no contractile vacuole. Endoplasm green in 

 color from enclosed chlorophyl. Habitat among aquatic 

 plants. Diameter of body 50 to 60 m- 



Fig. 360. Acanthocystis chaetophora. X 250. (After Leidy.) 



^M^MW^- 



175 (168) With a solid envelop, perforated for the pseudopodia. Sometimes 

 stalked Order Desmothoraca. 



One genus reported in North America. . . . Clathrulina Cicnkowsky. 



Envelop with a stalk. 

 Representative species Clathrulina elegans Cienkowsky 1867. 



Envelop more or less chitinous, perforated by numerous large, irreg- 

 ular openings. Protoplasm not filling the envelop. Nucleus single. 

 One or more contractile vacuoles. Pseudopodia very delicate, appar- 

 ently without a.Kial filaments. Habitat sphagnous swamps and among 

 aquatic plants; very common in some localities. Diameter of envelop 

 60 to 90 M- 



Fig. 361. Clathrulina elegans. X 130. (After Leidy.) 



IMPORTANT REFERENCES ON PROTOZOA, ESPECIALLY 

 SARCODINA 



BuTSCHLi, O. 1883. Protozoa. In Bronn's Klassen and Ordnungen des 



Thierreichs, vol. i, pt. 1-3. Leipzig. 

 Calkins, G. N. 1901. The Protozoa. New York. 



1909. Protozoology. New York. 

 Cash, J., and Hopkins, J. 1 905-1 909. The British Fresh-water Rhizopoda 



and Heliozoa. 2 parts. Ray Society, vol. 75. 

 COCKERELL, T. D. A. 1911. The Fauna of Boulder County, Colorado. 



Univ. Colo. Studies, 8: 227-256. 

 Conn, H. W. 1905. A Preliminary Report on the Protozoa of the Fresh 



Waters of Connecticut. State Geol. and Nat. Hist. Survey, Bull. 2; 



69 pp., 34 Pl. 



