426 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



MYCALE AEGAGROPILA (Johnston). 



Halichondria aegagropila Johnston, 1842, p. 119. 



Esperella aegagropila Vosmaer and Pekelharing, 1898, p. 19. 



Occurring as a thin incrustation, 350-500 y. thick, on a dendritic 

 alcyonarian taken at stations D5136 and D5145. 



The megascleres as a rule form the usual, short, more or less 

 vertical fibers running upward from the base and expanding at the 

 surface in wide brushes. But where the sponge is very thin, the 

 brushes alone stretch from base to surface. The tangential spicules 

 of the dermal membrane are arranged in tracts, several spicules thick, 

 forming a reticulum in which the side of a mesh is about equal in 

 length to a spicule. 



The megascleres are subtylostyles or styles, the two forms about 

 equally abundant, 250-280 by 7 p. The spicule tapers toward the 

 base as well as toward the point, and is often not quite straight. 



The anisochelas are 36-50 [x long. In the dermal membrane they 

 frequently occur in rosettes. Young stages are abundant down to 

 minute ones, 4 jx. long. 



The large toxas reach 160 jjl in length and occur singly. Smaller 

 sizes, especially a size about 50 [x long, are much more abundant. 

 These occur singly but also often in bundles, constituting toxo- 

 dragmas. 



The characteristic sigmas are 70-90 [x long ; smaller sizes abundant. 



The incrustations from the two stations seem to differ slightly, 

 as might be expected. At any rate in my preparations of material 

 coming from station 5145 the very large toxas and the large sigmas 

 are more abundant,, the anisochelas less abundant and smaller, than 

 in preparations of material from station 5136. 



Vosmaer and Pekelharing (1898, pp. 19-31) have shown that a 

 number of forms should be combined under this specific name, al- 

 though there is ground for objection to some of their mergings. The 

 species may be defined as a widely spread one generally occurring 

 as a thin incrustation, in which the characteristic combination of 

 spicules is as given above and in which the skeletal arrangement is, 

 in general, as given above. A full description with references to 

 the literature is given in Vosmaer and Pekelharing's paper. Doubt- 

 less many geographical varieties, differing in details, are distinguish- 

 able. Perhaps the incrusting sponges which Hentschel describes 

 (1911, p. 296) under Mycale macilenta, var. australis, from south- 

 west Australia may be regarded as such. In these sponges the 

 tangential dermal megascleres form a thick layer, and a second form 

 of anisochela, 12-20 [x long, differing in some details of shape from 



