BRITISH SPONGIAD.E. 177 



sometimes scarcely to be perceived. The largest of the an- 

 chorate spicula are by no means numerous ; both forms are 

 about equal in size ; the small ones are very minute, and 

 do not exceed about one third the length of the larger de- 

 scriptions of those organs, and they also are very few in 

 number, and are by no means easily detected in situ, even 

 when mounted in Canada balsam. Among the retentive 

 spicula, the contort bihamate ones are by far the most 

 numerous, and form one of the most striking characters of 

 the species ; they are about three times the length of the 

 largest of the anchorate ones, and are stout in proportion, 

 and they appear to abound in all parts of the membranous 

 tissues. 



17-Hymeniacidon fallax, Bdwerbank. 



Sponge. Massive, sessile; surface smooth, but uneven. 

 Oscula simple, dispersed. Pores inconspicuous, not 

 numerous. Dermai membrane thin, transparent, with 

 a dense, irregular stratum of spicula, attached to and 

 immediately beneath it. Skeleton. Spicula, acuate, 

 sub-fusiform, and rarely sub-spinulate. Interstitial 

 membranes : spicula of the same form as those of the 

 skeleton, but slender and flexuous. Sarcode abundant. 



Colour. Dried, light ash colour. 

 Locality. Torbay, Mrs. Griffiths. 

 Examined. When dry. 



The form of the only specimen I have seen of this species 

 is that of an irregularly compressed fig. It is an inch and 

 a half in height, by one inch in breadth, and does not ex- 

 ceed half an inch in thickness. I have designated it fallax 

 from the close resemblance that exists between its spicula 

 and those of Hymeniacidon Alderi, but the sub-spinulate 

 character is wanting in the latter species. 



If it should prove hereafter that the external form and 

 general character of //. fallax is tolerably constant, those 



12 



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