432 PROCEEDINGS OF THE ACADEMY OF [1898. 



.a much larger mass. The smaller may be unbranched and reach 

 a length of two inches, but are usually provided with a few small 

 branches. The larger are complexly branched, the secondary 

 branches usually forming angles of about 60° with the principal 

 branches, which latter arise from the central trunk at angles of 80°- 

 '90°. 



While the base and lower part of the stalk are perforated by 

 only a few small pores, the upper part has numerous conspicuous 

 oscula. They perforate the sponge wall between the larger bundles 

 of fibrous spicules, the outer flesh layers rising i of an inch as 7 

 delicate crater-like rims, scarcely thicker than a sheet of paper. 

 The oscula are usually elongated in the longitudinal direction of the 

 sponge, and in that case have a length of 5 to 6 mm., by a width of 

 2 to 3 millimeters. In such the rim flares out somewhat at the 

 sides and contracts at the ends, so that its outer edge has a nearly 

 circular outline. Some few of the oscula are circular at their 

 gastral ends. With regard to their distribution on the sponge 

 walls, the lower-most is situated 2 2 inches above the base, and its 

 rim is thickened like the neighboring sponge walls. Most of them 

 evidently stand in some relation to the larger branches. Three 

 occur at precisely the level where the largest spine arises, and two 

 near each of most of the other large branches. In many cases 

 the oscula lie directly at the bases of the large branches, their 

 orater-like rims being continuous on one side, most often above, 

 with the substance of the branch. Looking through the oscula on 

 to the gastral surface, this is seen to be formed of a fibrous network 

 of spicules, without the woolly surface covering of loose spicules. 



The specimen is a macerated one ; as I was unable to dissect 

 or section it, the arrangement of the chambers and the exact ar- 

 rangement of the spicules could not be determined. The bulk of 

 the skeleton of the sponge wall is, however, chiefly composed of 

 bundles of long fibre like diacts of various sizes and characters. 

 These are disposed in bundles which run longitudinally through the 

 sponge body, but divide and reunite in such a way as to form a net- 

 work, in the meshes of which the oscula open, and which raise more 

 or less evident ridges on both gastral and dermal surfaces. In the 

 upper part of the sponge these diacts remain free, but below they 

 are cemented together as above described. They exist in great 

 variety, but the majority have the form represented in Plate XX, 

 fig. 1, in which the transverse rays are reduced to minute nodules; 



