mass, on under sides of sticks and stones, in water pipes, etc.; statO' 

 blasts oval, with a brownish, cellular marginal ring 19. 



19. Apertures in cones that appear as swellings on the main branches 



Hyalmella punctata (Hancock) 

 Apertures at the ends of stems from the main branches 

 Plumatella repens Kraepelin 



20. Stem not jointed; statoblasts oval, without a cellular marginal ring 



Fredericella sultana (Blumenhach) 

 Stem jointed, or with partitions between the individual animals; statO' 

 blasts, in the familiar forms, oval, with a purplish, cellular marginal 

 ring 2 1 . 



21. Tentacles not completely retractile; no statoblasts known; rare 



UrnateUa gracilis Leidy 

 Tentacles completely retractile 22. 



22. Individual animals long-cylindrical, arising erect from a stem; no statO' 



blasts known; rare 



Pottsiella erecta (Potts) 

 Individual animals attached directly to each other in a more or less branch' 

 ing arrangement; statoblasts oval, with a purplish, cellular marginal 

 ring; on the under sides of stones, etc.; common 



Paludicella articulata (Ehrenberg) 



GENERAL REFERENCES 



Annandale, N. 1910. Fresh-water Sponges in the Collection of the United 

 States National Museum. Proc. U. S. Nat. Mus., Vol. 37; Pg. 401-406. 



Davenport, C. B. 1918. Moss Animalcules. Chap. 28 in Ward and 

 Whipple's "Fresh-water Biology". John Wiley ^ Sons. New York. 



Hyman, L. H. 1929, 1930 and 1931. Taxonomic Studies of the Hydras of 

 North America. In 3 parts. Trans. Amer. Micros. Soc, Vols. 48, 49 

 and 50. 



Old, M. C. 1932. Delaware Fresh-water Sponges. Trans. Amer. Micros. 

 Soc, Vol. 51. 



Payne, F. 1924. A Study of the Fresh-water Medusa, Craspedacusta ryderi. 

 Jour. Morph., Vol. 38; Pg. 387-430. 



Potts, E. 1887. Fresh-water Sponges. Proc. Acad. Nat. Sci. Phila., Vol. 

 39; Pg. 158-279. 



Potts, E. 1918. The Sponges. Chap. 10 in Ward and Whipple's "Fresh- 

 water Biology". John Wiley ^ Sons. New York. 



Rogick, M. D. 1940. Studies on Fresh-water Bryozoa. Trans. Amer. Micros. 

 Soc, Vol. 59, Pg. 187-204. 



Smith, F. 1918 Hydra and Other Fresh-water Hydrozoa. Chap. 11 in Ward 

 and Whipple's "Fresh-water Biology". John Wiley & Sons. New York. 



Smith, F. 1921. Distribution of the Fresh-water Sponges of North America. 

 Bull. 111. Nat. Hist. Surv., 14; Pg. 13-22. 



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