348 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Color of the clean upper surface whitish, the marginal region 

 in most specimens marked off. as a somewhat translucent ring, from 

 a central more opaque region which indicates the extent of the 

 choanosome. Diameter of the bod} 7 varies from 9 to 20 mm. In 

 a representative lens-shaped specimen, the body diameter is 15 mm., 

 thickness at the center 6 mm. In one of the conical specimens, the 

 diameter is 11 mm., the central thickness 8 mm. The marginal 

 fringe is 6-9 mm. wide. 



Probably the body can change its shape to a limited extent. At 

 any rate, the fringe is inclined much more sharply toward the 

 oscular face in some specimens than in others, and the marginal 

 region of the sponge bod} 7 in some specimens inclines distinctly in 

 that direction. 



As to the natural position of the sponge, Ridley and Dendy, 1887 

 (p. 218), infer that the oscular face is always the upper, and that 

 therefore in one of their two species the fringe spicules project up- 

 ward, in the other species downward. Vosmaer (1885, pi. 1) rep- 

 resents his sponges as resting on a substratum by means of the 

 spicular fringe, but with the oscula on the upper surface. It is not 

 impossible, however, that in sponges so resting the oscular face may 

 be directed downwards (the position of the animal would then be 

 rather loosely analogous to that of bottom-living medusae such as 

 certain Rhizostomes), in which case my figure (pi. 48, fig. 1) should 

 be turned. In Ilallcnemki patera. Bowerbank (1866, p. 96) regards 

 the oscular face as the under one. In the physiologically somewhat 

 parallel case of the Crinorhiza sponges, Ridley and Dendy think 

 the radiating marginal processes project downward, thus serving 

 to hold up the sponge on a muddy bottom. But Topsent (1902) 

 argues that, at any rate in some Crinorhiza forms, these processes 

 project upward. 



On bisecting the sponge it is seen (pi. 48, fig. 1) that the ectosome 

 is colorless and so thick that the loose brown choanosome (ch) 

 occupies only about one-third of the central thickness of the sponge. 

 The oscular canals (o. c.) are simple tubular canals, 350-500 pi wide 

 leading from the choanosome. through the cortex, each to an osculum. 

 Each canal is immediately surrounded by ascending radial skeletal 

 bundles. 



The spicules are fusiform tylostyles that vary in size in the dif 

 ferent regions of the body. The head is small but usually well de 

 veloped, although the spicule not infrequently becomes a subtylo 

 style. 



The cortex of the upper (oscular) face, in respect to its skeleton, 

 is distinctly stratified (pi. 48, fig. 1). (a) The superficial stratum, 

 about 600 \l thick, is composed of closely set short tylostyles, about 

 500 by 12 fx, radially placed and projecting slightly at the surface. 



