430 THE DEPTHS OF THE SEA. [chap. vii. 



of the sponges dredged from Mr. Marshall Hall's 

 yacht.' 



Sponges belonging to other groups from the deep 

 water were nearly equally interesting. I have 

 already alluded, p. 188, to the handsome branching 

 sponges belonging to the Esperadise, which abound 

 off the coasts of Scotland and Portugal. Near the 

 mouth of the Strait of Gibraltar a number of species 

 were taken in considerable quantity, belonging to a 

 group which were at first confused with the Hexac- 

 tinellidse, on account of their frequently forming a 

 similar and equally beautiful continuous network of 

 silica, so as to assume the same resemblance to deli- 

 cate lace when boiled in nitric acid. The Corallio- 

 spongise differ, however, from the Hexactinellidae in 

 one very fundamental character. While in the latter 

 the spicule is hexradiate, in the former it consists 

 of a shaft with three diverging rays at one end. 

 The^e frequently spread in one plane, and they often 

 re-divide, and frequently the spaces between them are 

 filled up with a secondary expanse of silica, variously 

 frilled and netted on the edge, so as to give the spicule 

 the appearance of an ornamental flat-headed tack. 

 These three-rayed stars or disks, in combination, sup- 

 port the outer membrane of sponges of this order; 

 and spicules of the same type, fused together accord- 

 ing to various plans, form the sponge skeleton. 



This group of sponges are as yet imperfectly 

 known. They seem to pass into such forms as 

 Geodia and Tethya ; and the typical example with 

 which we are most familiar is the genus Dacty- 

 localyx, represented by the cup-shaped pumice-like 

 1 Monthly Microscopic Journal, November 1, 1870. 



