212 Tir.J.E.Giiiyon the 



luis shown the. chan^-c of form in tlic elongated clasping basal 

 or rooting spicules of tliis group in Rossella, where the spicules 

 often have, as well as the four recurved lateral rays {I. c. 

 (t. xxi. f. 2), the shaft produced beyond the lateral rays, as in 

 t. xxi. f. 1, 3. 



In some, especially of the superficial sexradiate spicules, 

 the arms of the different spicules are placed so that the arms 

 of the neighbouring spicules are parallel to each other ; but in 

 some sponges they are oblique, compared with the axis of the 

 sponge, and in others they are perpendicular and transverse to 

 the axis of the sponge, producing rhomboidal or rectangular 

 areola? on its surface, which are especially visible when the 

 arms of the neighbouring ones, which form the square areolae, 

 coalesce and form a solid network, as in the genus Farrea 

 (B. S. t. XV. f. 277, t. xxi. f. 311, which represents a part from 

 the interior of a sponge which has the axis of the spicules 

 developed at both ends). 



Most of the spicules of this division are smooth ; but Dr. 

 Schultze figures several varieties of forms which have the arms 

 more or less tuberculated (Hyalonema, t. iii., t. iv. f. 6), and 

 others, which are scattered, with elongated acute spines directed 

 from the centre (Hyalonema, t. iv. f. 2, 4, 7, 8, 9, all being 

 figured from one sponge, and showing the folly of naming 

 spicules in Dr. Bowerbank's way). 



The elongate tapering rays of the spicules of this form are 

 sometimes furnished with a branch on each side not far from 

 the base (B. S. t. viii. f. 188, 189), which form a passage to 

 the more stellate spicules of this group (see B. S. t. viii. 

 f. 188, " bifurcated rectangulated hexaradiate stellate spi- 

 cules," and t. viii. f. 189, " trifurcated attenuato-hexaradiate 

 spicules "). These spicules show the passage between the long- 

 armed forms and the short divided-rayed ones which follow. 



Many sexradiate spicules, instead of having long, conical, 

 tapering, acute axes and rays, have all the rays short and of 

 equal length, sometimes terminating in a kind of cup (B. S. 

 t. viii. f. 196, "pocillated hexaradiate stellate spicule"), or in 

 a broad expansion deeply divided into lobes (B. S. t. viii. 

 f. 195, called " coronato-hexaradiate stellate spicule "). In 

 others each ray of the spicule ends in a cluster of four or more 

 elongate linear arms, ending in a tubercle (B. S. t. viii. f. 190- 

 192). They are called spinulo-trifurcated, spinulo-quadri- 

 furcated, and spinulo-multifurcated hexaradiate stellate spi- 

 cules. In others the rays terminate, like the former, in a 

 group of linear arms ; but they assume a bell-shape, and each 

 lobe is dentatcd and rcflexcd at the end (B. S. t. viii. f. 193, 

 194), and arc called floricomo-hexaradiate spicules. 



