2 PROCEEDINGS OF THE NATIONAL, MUSEUM vol, S2 



The space thus formed in this region between the inner and outer 

 chitinous coats is filled with the air cells. In the regions where the 

 two coats separate the air cells are in a single layer (fig. 3, c), but 

 as the coats become more widely separated the cells are in several 

 layers. This granular zone ranges from 48/* to 56/* in thickness. It 

 is not charged with, nor is the gemmule surrounded by, gemmuie 

 spicules. 



Skeletal spicules. — There are two types of skeletal spicules, both 

 of which are spined. Those of one type, Avhich are the more abun- 

 dant, are slender and slightly curved. They taper to sharp points 

 at both ends and bear numerous minute spines. These spines are 

 perpendicular to the spicule at the center, but on each side of the 

 center they are curved toward their respective ends of the spicule 

 (fig. 8). While many of these spicules lie singly in the parenchyma, 

 the majority are collected into bundles, which mark out a rough 

 framework for the sponge. These bundles contain 2 to 10 spicules. 

 Spicules of this type range from 185/* to 245/* in length by 3.9/* to 5.8/* 

 in width. Those of the other type of skeletal spicule are straight 

 and taper toward points at both ends. They bear prominent spines, 

 which are subdivided at their extremities into 2 or 3 smaller spines 

 (fig. 7). These spicules range from 135/* to 143/i in length by 3.5/^ 

 to 4.4/* in width. They are not abundant. 



Dermal spicules. — These are small equibirotulates. Each rotule 

 consists of a small inturned disk bearing 6 or 8 curved hooks, which 

 are directed toward the rotule at the opposite end of the spicule. 

 The shafts may be either straight or curved. They are entirely free 

 from spines (fig. 9). These small birotulates measure from 19/* to 

 27/* in length by 1.75/i in diameter. The rotules range from 5,u 

 to 7/* in diameter, including the hooks. These spicules are abundant 

 in all specimens but are especially so in young sponges. 



Flesh spicules. — There are two types of flesh spicules, both of 

 which are equibirotulates. In one type the rotules consist of 4 or 6 

 incurved hooks. The shafts are straight and bear several slightly 

 curved spines, which are as long as the hooks of the rotules (fig. 4). 

 These spicules measure 45/* to 55/* in length by 2.6/i to 3.8/* in 

 diameter. The rotules are 8.7/* to 10.4/i in diameter. Both types of 

 flesh spicules are abundant, but the type just described is more 

 abundant than the following one. The rotules of the other type are 

 knoblike and bear numerous spinelike rays, which are not all at 

 one level (figs. 5, 6). The shafts are straight and may bear 1 or 2 

 minute spines. These spicules range from 35/* to 45/* in length by 

 3> in diameter. The rotules range from 11/* to 20/i in diameter, 

 including the spines. 



