RHABDOCALYPTUS MOLLIS. 261 



The internal surface of the sponge-wall is covered tlirougliout 

 with a continuous gastral lacework, in which the meshes, for the 

 most part regularly quadrate in shape, can be discerned with 

 the naked eye (PL XX., fig. 13). Beneath the layer are seen 

 hypogastral strands varying in thickness, running in indefinite 

 directions and intersecting one another at various angles. 



The canals, both incurrent and excurrent, are deep and pit- 

 like. In the larger specimens, the roundish canalar apertures of 

 the incurrent system may be as large as 4 or 5 mm. in diameter, 

 while those on the gastral surface measure at most 2 mm. The 

 latter are thus on the wdiole smaller than the former but are 

 situated more closely together (PI. XX., fig. 2). On cross-sections 

 of the sponge-wall, the canals of the two systems do not alternate 

 so regularly as in certain other species in which they are of ap- 

 proximately the same caliber. 



Spiculation. 



With F. E. Schulze's excellent descriptions of the spicula- 

 tion of this species and with two slide preparations from the type 

 specimen which he gave me, it was an easy matter for me to 

 recognize the species. 



The principal parenchymalia are bow-like oxydiactins which 

 may be 20 mm. long and 90 /^ thick in the middle but are more 

 generally smaller. The middle is not externally marked by 

 swellings. The rays are gradually attenuated toward the end. 



The smaller parenchymalia, down to comitalia of only 4 /^ 

 thickness, are of the usual description. A central nodal thickening 



