124 U.S. NATIONAL MUSEUM BULLETIN 272 



teeth, representing distinctly umbonate rotules; size differences of 

 the two classes either negligible or very distinct. 



Gemmules rather scarce, large and spherical; pneumatic coat well 

 developed, consisting of minute air spaces, often somewhat granular; 

 gemmoscleres embedded within this layer radially, the longer class 

 protruding from the outer gemmular membrane. 



Sponges forming extremely delicate and small encrustations on 

 aquatic plants. Coloration always vivid green, owing to the presence 

 of zoochlorellae. Consistency very soft and fragile. 



Discussion. — The genus Corvomeyenia was loosely introduced by 

 Weltner (1913) to include those freshwater sponges which, in addition 

 to their bu'otulate gemmoscleres, possess minute birotulate micro- 

 scleres in both their symplasm and dermal membrane. Apart from the 

 species Meyenia everetti Mills, designated by Jewell (1952), two ad- 

 ditional sponges of highly dubious identity, Spongilla novae-terrae 

 Potts and Spongilla discoides Penney, were also included in this genus. 

 However, the present investigations revealed beyond doubt that their 

 retention in this genus is fully unwarranted. 



The dubious identity of S. novae-terrae is best demonstrated by the 

 difficulty of authors to document its generic position, since this 

 "species" has alternatively been listed as belonging to Spongilla and 

 Ephydatia (= Meyenia), as well as to Corvomeyenia and Corvospongilla. 

 The reexamination of its type slides made it quite clear that it cannot 

 be considered a distinct species, but that it represents a hybrid of 

 C. everetti and a species of another not clearly recognizable genus, 

 possibly Eunapius or Spongilla. The presence of unmistakably 

 typical microbirotulates of C. everetti in the spicular mixture of S. 

 novae-terrae and the grossly malformed gemmoscleres are proof of a 

 sexual hybridization between the former species and that of some other 

 genus, rathei;" than a mere ecomorphic variation of the latter. 



The inclusion of S. discoides Penney in the present genus has been 

 aided by the incorrectness of its original description and by the 

 presence of distinct microbirotulates. Jewell (1952), using Penney 's 

 original description, found the apparent presence of two classes of 

 "flesh spicules" important enough to erect a new genus, Parameyenia. 

 Penney (1957), while correcting his earlier mistake in recording ab- 

 normal disklike gemmules of this species, placed it into Corvomeyenia 

 in spite of the absence of gemmules in the only specimen found. The 

 reexamination of the type of S. discoides (USNM no. 22194) during 

 the present studies made it clear that this species contains some, 

 probably adventitious, microbirotulates of C. everetti or a closely 

 allied species, but that the remainder of its spicular components are 

 those of Anheteromeyenia ryderi, claimed by Penney (1933) to occur in 

 the type locality of S. discoides. The two types of "flesh spicules" 



