NORTH AMERICAN PORIFER^. PART II. 545 



besides this tlie membranes everjrwhere, and the internal portions of the sarcode. This 

 characteristic therefore has greater significance tlian in any other species, and justified the 

 retention of the distinct generic name of Dysidea. 



Dysidea fragilis Johnst. 



Dysidea fragilis Johnst., Brit. Spon., p. 286. 



Dysidea fragilis Bow., Brit. Spong., p. 381, pi. 13, 14. 



This species (PI. xvii, fig. 17) resembles Johnston's Dysidea fragilis, but evidently has 

 a much coarser mesh, and probably grows larger. Its color when living is not known. 

 Otherwise the specimen corresponds quite closely to the descriptions of Johnston. The 

 skeleton (PI. xvii, fig. 18) is similar to that of Spongelia, but presents characteristics which 

 ally it closely with Hircinia. There is a tendency to branch in the primary fibres, and 

 they are often compound. The secondary fibres are sometimes single and hairy, and some- 

 times composed of the usual mass of cellular or perforated fibres as in Hircinia. The 

 membranes are loaded with foreign materials, and so also are the primary and secondary 

 fibres, with the exception of the single dark horn-colored ones allude"d to above. The sur- 

 face is rather rough, with the slightly projecting points of the primary fibres covered with 

 hardened sarcode. The whole mass when dried is very light and porous, and of a flat, 

 tabulate shape. The excurrent orifices are few and rather small. When carelessly dried 

 these entirely disappear, and the specimens become very hard. 



Loc, Zanzibar, in Coll. Peabody Academy ; Biscayne Bay, in Soc. Coll. Specimens in 

 the Coll. Mus. Comp. Zool. are named Spongelia? by Schmidt. 



HiKCixiA Nardo. 



Filifera Lieb. 



Sarcotragus Schmidt. 



Polytherses Duch. et Mich. 



This genus is pecuharly liable to the attacks of a seeming parasite, which forms a fila- 

 mentous tissue often connecting all the fibres of the sponge with a sheet-like net-work. The 

 filaments disappear ui a completely macerated sponge, or if pi-esent, present a hollow tubu- 

 lar aspect with a bulb at one end, as figured by Schmidt. In less completely macerated 

 specimens the contents are visible in the interior of the threads, and are broken up, looking 

 in some specimens hke cells. This may be erroneous, but certainly these threads are not 

 constituted like regular sponge fibres, and are probably parasites of some sort, but 

 whether Alg^e or not, it is difficult to determine. 



Carter describes it as an Alga, under the name of Spongiopliaga communis, and says 

 that he has foimd it in other sponges than Hirciniae. Neither Schmidt nor others have, how- 

 ever, quoted any similar instances, nor has Carter given the names of the other species. 

 Schmidt is evidently very doubtful, but is inclined to the same view as Kolliker, that the 

 filaments are distinct elements from the fibres, and this is also my own impression. The fila- 

 ments are much larger than the fibrillae, the color and aspect when dried distinct, and the 

 former never have the little bag on the end. 



MEMOIRS BOST. SOO. NAT. HIST. VOL. 11. 137 



