BRITISH SPONGIAD^. 133 



more or less clavate at their terminations, and are fre- 

 quently somewhat flexuous. 



The skeleton columns are short. They are composed of 

 stout attenuato-acuate, entirely and strongly spined spicula 

 well cemented together by keratode. The whole of the 

 spicula do not spring from the basal membrane, a portion 

 of them being successively produced in the course of the 

 development of the skeleton, and the column frequently 

 terminates with four or five of them radiating at various 

 angles. The skeleton spicula vary considerably in size. 

 One of the longest measured ^y^d inch in length, but the 

 greater part of them range from jijth to gsgth inch in length. 

 The spination of the spicula is very abundant, and the 

 spines strongly produced, especially at the base of the 

 spiculum, where they frequently exceed in length half its 

 greatest diameter. - The retentive spicula in this species 

 are very characteristic, but as they are both few in number 

 and very minute, they are not readily detected, either 

 in situ, after immersion in Canada balsam, or by the dis- 

 solution of a portion of the sponge in nitric acid. They 

 require a microscopical power of about 600 linear to define 

 them distinctly. The average length of the anchorate spi- 

 cula is ligoth inch, while the unipocilate and bipocilate ones 

 do not exceed 3530th inch in length. Each form prevails 

 to about an equal extent, and the greater number of them 

 appear to be seated on the basal membrane. 



6. MicRocioNA OARNOSA, Bowerhanh. 



Sponge. Coating ; surface even, smooth. Oscula simple, 

 dispersed. Pores inconspicuous. Dermal membrane 

 pellucid, spiculous ; spicula fusiformi-acerate, dispersed 

 or loosely fasciculated, numeroijs. Skeleton. Columns 

 long, slender, flexuous ; abounding in spicula, fre- 

 quently giving off single branches ; spicula sub- 

 attenuato-acuate, entirely spined ; stout and long ; 

 spines conical. Internal defensive spicula ; attenuato- 

 acuate, entirely spined, shorter than those in the 



