148 A MONOGRAPH OF THE 



double purpose of skeleton and defensive spicula ; their 

 bases are attached to the basal membrane of the sponge, 

 and their direction is always at nearly right angles to it. 

 They vary in length from ~th inch to ^th inch, and their 

 structure is very remarkable ; the clavate base is largely 

 and strongly produced, while the shaft attenuates rapidly, 

 and terminates in an extremely slender apex in the longest 

 of them, while the shorter ones are much stouter in their 

 proportions. This great inequality in length renders them 

 very much more effective in their character of external de- 

 fensive organs. Intermixed with the large attenuato-clavate 

 spicula there are a few extremely slender acuate ones, but 

 as their basement and their direction is precisely the same 

 as jthe larger ones, I believe them to be only a very early 

 stage of their development. 



The internal defensive spicula, like the skeleton ones, are 

 planted in the basal membrane, and their general direction 

 is at about right angles to it. They vary in height from 

 g^th inch to ^th inch, and their form is much like that of 

 a Florence oil-flask with an elongated neck, and an orna- 

 mental stellate stopper, the stout conical radii or spines 

 passing off in every direction, but emanating only from the 

 apex of the spiculum. The spines terminate acutely, and 

 their height is about twice that of their basal diameter. 

 These spicula are not readily to be detected when the sponge 

 is immersed in water, and it is only after immersion in 

 Canada balsam that they become distinctly visible. 



I subsequently received from the Rev. A. M. Norman a 

 small branch of Nullipara calcarea ? about four lines in 

 length, and one and a half in diameter, covered with this 

 sponge. The colour was much deeper and more inclined 

 to red than that of Mr. Barlee's specimens. It was obtained 

 by dredging off the Isle of Cumbrae, in the Frith of Clyde. 

 It has also been obtained from the Moray Frith, by the 

 Rev. Walter Gregor, late of Macduff. The specimens sent 

 to me by that gentleman were in very fine condition, and 

 the colour was a bright orange-yellow. There were three 

 on the fragment of a large bivalve shell, but no one exceeded 

 an inch in diameter. 



