REVISION OF FRESHWATER SPONGES OF SPONGILLIDAE 127 



and symplasm, either distinct asters, usually with rays arising from a 

 central spherical nodule, or rough amphioxea which in their central 

 portion bear a number of long perpendicular radiating rays, or a com- 

 bination of both of these types. 



Gemmoscleres of either slightly or markedly differing length groups, 

 in the latter case of two distinct classes, never of equal length ; they are 

 stout birotulates with strongly spined shafts and terminally with 

 distinctly umbonate rotules of equal diameter, their margins incised 

 into a nimiber of recurved teeth. 



Gemmules usually very abundant, scattered in the skeletal mesh- 

 work, large and always subspherical, often distinctly ovoid; pneu- 

 matic layer consisting of minute spherical air spaces; gemmoscleres 

 with their upper rotules often protruding through outer surface of 

 this layer; foramen produced into a short and straight tubule. 



Sponges often large and spherical with a rather uneven and lobose 

 surface, giving them a feathery appearance; oscula smaU but con- 

 spicuous, dermal membrane weU developed. Skeleton consisting of 

 defined radial spicule fibers, and an irregular arrangement of slightly 

 coherent transverse fibers. Consistency moderately soft but very 

 fragile. Coloration varying from green to brown. 



Distribution distinctly discontinuous, most species apparently 

 preferring tropical and subtropical climates. 



Discussion. — As mentioned in other sections of this paper, the 

 erectionof Pott's (1887) genus Heteromeyenia, a heterogeneous assem- 

 blage of not always related spongillid species, had its most regrettable 

 taxonomic consequences right to the present day. The system of 

 Potts failed to provide for microscleral criteria as distinguishing 

 featiu*es, characters of utmost importance for the reliable assessment 

 of the intergeneric relationship, regardless of an apparently similar 

 shape or arrangement of the gemmoscleres. This failure, together 

 with the ensuing division of the "Meyeninae" into species with 

 homogeneous and heterogeneous bu'otulates by later authors, led to 

 an artificial generic split of many closely related species. While D. 

 plumosa, D. palmeri, and D. brouni were thought to possess one 

 length group of birotulates and retained in Ephydatia {=Meyenia), 

 H. radiospiculata MiEs and H. plumosa Weltner with their conspic- 

 uously differing two length groups of birotulates were relegated to 

 species of Heteromeyenia. 



In his justified desire to separate H. radiospiculata and H. palmeri 

 on account of their stellate microscleres from Heteromeyenia, Annan- 

 dale (1912a) added to the confusion by his erection of a new genus. 

 Aster omeyenia, for their inclusion. Schroder (1927b), realizing the 

 intrageneric relationships within Heteromeyenia, made the first 

 attempt to subdivide Pott's genus into a number of more natural 



