of some Cakareoiis Spmiges. 169 



handle. The quadriradiate spicula are generally very minute, 

 and in number about one to a hundred of the triradiate. The 

 third kind of spiculum in this species, is a very minute straight 

 equally thick spiculum, obtuse at both ends, and generally about 

 the fiftieth of a line in length ; this form is very abundant, and 

 may possibly be derived from the broken rays of very small tri- 

 radiate spicula, as in the compressa. These three kinds of spi- 

 cula are likewise calcareous, and dissolve with rapid efferves- 

 cence on being touched with diluted nitric acid. On looking 

 closely into the surface of the S. nivea, with a single lens, we 

 perceive that the large triradiate spicula lie parallel with the 

 surface, and contribute to form and protect the pores. 



In a portion of the Spongia complicata of Montagu, sent me, 

 along with fragments of nearly thirty other species of British 

 sponges, by the Rev. Dr Fleming of Flisk, who has collected 

 and studied the British zoophytes for upwards of twenty years, 

 I observe the axis to consist entirely of very minute triradiate 

 spicula, which dissolve rapidly with effervescence, when touched 

 with nitric acid. Dr Fleming mentions this species as an inha- 

 bitant of the Frith of Forth, and considers it a variety of the 

 S. hotryoides of most authors. The triradiate spiculum not 

 only occurs alone, and very small, in this species, but is quite 

 peculiar and very imperfect in its form ; the rays are very 

 short and disproportionally thick ; they often diverge at unequal 

 angles, and, on viewing the spiculum sideways, they are seldom 

 found to lie in the same plain. This sponge has a white colour, 

 like the other calcareous species, and, when dry, the spicula on 

 its surface have the same shining silvery lustre. The triradiate 

 spicula of the S. hotryoides were figured and described by Mr 

 Ellis, and have been mentioned by most writers since his time. 

 Montagu and Lamouroux have very judiciously introduced the 

 forms of the spicula into their definitions of this species ; and in 

 order to distinguish them from the triradiate spicula of the 

 S. complicata^ Montagu mentions that they are more than four 

 times as large as those of the latter sponge. From having inva- 

 riably found the triradiate spiculum present, either alone or com- 

 bined with other forms, in calcareous sponges, I have no doubt 

 that the true S. hotryoides, if distinct from S. complicata, will 

 be found to have a calcareous axis. A portion of another 



