430 THE DEPTHS OF THE SEA. [CHAP. 1X. 
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 Esperiadee, 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 
eroup which were at first confused with the Hexac- 
tinellidee, on account of their frequentiy 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- 
spongie differ, however, from the Hexactineilidee in 
one very fundamental character. While in the latter 
the spicule is hex-radiate, in the former it consists 
of a shaft with three diverging rays at one end. 
These 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 Dactylo- 
calyx, represented by the cup-shaped pumice-like 
1 Monthly Microscopic Journal, November 1, 1870. 
