102 BEITISH SPONGIAD.E. 



which are the most numerous, measured YocTo mcn ^ n 

 length. 



" The rete of the skeleton structure is tolerably 

 symmetrical, and is generally composed of three or 

 four spicula fasciculated together ; the spicula are short 

 and stout ; their spination is not very strongly pro- 

 duced, and it is usually confined to the base and apex 

 of the spiculuni, but occasionally a few spines are 

 developed between the two terminations. The inter- 

 stitial membranes are very sparingly supplied with 

 tension spicula, which are so slender as to readily 

 escape observation, and a few retentive spicula, the 

 same as those of the dermal membrane, are occasionally 

 observed. 



" The great abundance of the hastate dermal spicula 

 and their peculiar mode of disposition, combined with 

 the singular forms of the tridentate, equi-anchorate, 

 retentive ones, readily distinguish this species from 

 several other closely allied British species." 



17. HALICHONDKIA CONDENSA, Bow., n. sp. 3 iv, Plate VI, 

 figs. 13. 



" Sponge sessile, rising, and branching irregularly, 

 compressed. Surface smooth and even. Oscula simple, 

 marginal, tuberculate. Pores inconspicuous. Dermal 

 membrane reticulated, rete monospiculous. Areas 

 mostly triangular, rarely quadrangular, one spiculum 

 in width ; spicula acerate, short and stout, same as 

 those of the skeleton. Skeleton very much condensed 

 and complicated ; rete multispiculous, loosely fascicu- 



