322 FRESH-WATER BIOLOGY 



11 (12) Hydranth form most frequently seen; medusae rarely found and 



have but eight tentacles Microhydra Potts. 



But one species, M . ryderi Potts, 

 first described from near Philadel- 

 phia, Pa., but since then found in 

 different localities in Europe. The 

 medusae have been seen only when 

 in a very early stage and the adult 

 stages are not known. 



FIG. 587. Microhydra ryderi. (a) Young 

 medusa. X 40. (After Moore from 

 Potts.) (b) Hydranths and embryo. 

 X 22. (After Ryder from Potts.) 



12 (n) Hydranth form rarely seen; medusae have more than eight tentacles. 



Craspedacusta Lankester. 



But one species, C. sowerbyi Lankester, known in Europe 

 and America. Found only in aquaria according to earlier 

 records, but large numbers were collected by Professor H. Gar- 

 man in September, 1916, in a creek near Frankfort, Kentucky, 

 the first record of their occurrence in other than artificial sur- 

 roundings. A. second species, C. kawaii Oka, has been found in 

 a river of China. 



FIG. 588. Craspedacusta sowerbyi. X about 4. (After Hargitt.) 



Limnocnida Giinther is the only other known genus of fresh-water medusae and its 

 distribution so far as recorded is limited to the Eastern Hemisphere. Limnocnida 

 tanganyicae (Bohm) 1883 is found in Africa; Limnocnida indica Annandale 1912, in 

 India; Limnocnida rhodesia Boulenger 1912, in southern Africa. 



IMPORTANT REFERENCES ON FRESH-WATER HYDROZOA 



BRAUER, A. 1909. Die Benennung und Unterscheidung der Hydra-Arten. 



Zool. Anz., 33: 790-792. 

 DOWNING, E. R. 1905. The Spermatogenesis of Hydra. Zool. Jahrb., Anat., 



21 : 379-426. 

 HARGITT, C. W. 1908. Occurrence of the Fresh-water Medusa, Limnoco- 



dium, in the United States. Biol. Bull., 14: 304-318. 

 NUTTING, C. C. 1901. The Hydroids of the Woods Hole Region. U. S. 



Fish Com. Bull, for 1899: 327. 

 POTTS, E. 1906. On the Medusa of Microhydra ryderi and on the Known 



Forms of Medusae inhabiting Fresh Water. Quar. Jour. Mic. Sci., 50: 



623-633; 2 pi. 

 SMITH, F. 1910. Hydroids in the Illinois River. Biol. Bull., 18: 67-68. 



