BRITISH SPONGIAD^. 89 



spaces. The whole of the connecting spicula are large 

 and stout, with the radii very short, and abruptly bent 

 backwards. In the canals which pass through the centre 

 of the radii from base to apex there is frequently a small 

 globular dilatation at about half their length, and occa- 

 sionally the same canals assumed a somewhat moniliforra 

 character, but whether these minute peculiarities are acci- 

 dental or specific it is difficult to say from a single specimen. 

 The external defensive spicula are few in number, and not 

 very regularly disposed. The stellate spicula "abound most 

 near the surface of the sponge, and especially the larger 

 ones, and the membranes lining the large confluent inter- 

 marginal cavities are thickly studded with them ; the three 

 varieties of their form are intermixed near the surface, but 

 in the deeper portions of the interstitial membranes the 

 cylindro-stellate form prevails to a greater extent than the 

 attenuato-stellate ones. 



Since the above description was written I have received 

 a small fragment of this species from my friend, Mr. Gosse, 

 who " picked it from the under-eide of a boulder at Round- 

 stone Head, near Paignton, Torbay." It agrees in every 

 structural character with the specimen I found at Sark. 



T. Collingsii and T. Schmidtii closely resemble each 

 other, both in external appearance and in structure, but 

 they may, when, mounted in Canada balsam, be readily 

 separated by the difference in form of the external defensive 

 spicula. In the former they are acerate ; in the latter they 

 are spinulate. 



I have dedicated this species to Mrs. Collings, the lady 

 of the Seigneur of Sark, to whose active researches in marine 

 natural history we are indebted for our knowledge of the 

 species. 



3. Tjsthea Schmidtii, Bowerbank. 



Sponge. Massive, sessile, depressed. Surface minutely 

 hispid. Oscula and pores inconspicuous. Dermis 

 thick and dense. Dermal membrane abundantly spi- 

 culous ; tension and external defensive spicula of the 



