BRITISH SPONGIAD^. 261 



the angles, and the basal tooth the third one, all three 

 being very small, while the apical palm extended over more 

 than half the length of the spiculum. The relative pro- 

 portions of the bidentate inequi-anchorate ones are very 

 similar to those of the palmated anchorate spicula ; both 

 sorts were attached to the derm.al membrane by the ex- 

 ternal surface of the middle of the shaft, and not by the small 

 basal end as in cases where such forms are congregated in 

 rosette-like groups. 



The skeleton spicula vary somewhat in the amount of 

 their spination ; sometimes they are only basally spined, and 

 occasionally the middle of the shaft exhibits an incipient 

 spination, but the general character of the spination is 

 basally and apically. The large fusiformi-cylindrical ten- 

 sion spicula are very abundant in the interstitial portions 

 of the sponge, crossing the areas of the skeleton in every 

 direction, and sometimes becoming associated with the 

 skeleton spicula in its network. The internal defensive 

 spicula are not half the length of the skeleton ones ; their 

 spination is complete and more prominent, especially at 

 the base. 



22. Halichondria Batei, Bowerbank. 



Sponge. Massive, sessile. Surface smooth. Oscula 

 simple, dispersed. Pores inconspicuous. Dermal 

 membrane spiculous ; spicula acuate, apices obtuse ; 

 loosely fasciculated. Skeleton. Spicula acuate, stout ; 

 entirely and profusely spined ; spines minute. Re- 

 tentive spicula very large ; and small, bidentate equi- 

 anchorate, rarely tridentate, very numerous. 



Colour. — Light brown in the dried state. 

 Habitat. — Shetland ? Mr. Spence Bate. 

 Examined. — In the dried state. 



This sponge is a small irregular mass, seated on a piece 

 of stone near the base of a specimen of Isodidya in- 



