PLATE LXX1V. 209 



tliat of the nodulous amorphous specimens of Hali- 

 chondria panicea, when it is parasitical on slender 

 branching fuci and it may readily be mistaken for that 

 species ; and especially if we view its surface by the 

 aid of a two-inch lens, when it presents to the eye very 

 much the same minute reticulation that is so charac- 

 teristic in H. panicea. A section at right angles to the 

 surface from the dried specimen exhibits a slight 

 degree of hispidation arising from the protrusion of the 

 terminations of some of the fasciculi of the skeleton 

 through the dermal membrane, but it is very probable 

 that that character would not be perceptible in a 

 living specimen. The difference in the forms of the 

 spicula at once separates the two species. 



The rete of the dermal membrane is very like that 

 of Hal. panicea, but the network appears to contain a 

 greater number of spicula of the same size and form as 

 those of the skeleton. In the specimen in course of 

 description the pores were abundant, and in an open 

 condition. 



The trenchant contort bihamate retentive spicula, 

 are among the most remarkable of the specific charac- 

 ters of this sponge. They are usually attached at the 

 back of one of the hooks to the rete of the skeleton 

 structure, while the other end is projected into its in- 

 terstices. The cutting edges of the trenchant parts 

 of the spiculum appear to be exceedingly sharp. They 

 very closely resemble those of Hymedesmia Joknsoni 

 represented in Plate v, fig. 112, vol. i, 'Monograph of 

 British Sponges,' both in size and form. They are 

 exceedingly few in number, and may easily escape the 

 notice of a hasty observer, and they are most readily 

 detected in a preparation of the spicula by boiling in 

 nitric acid. 



HALIOHONDEIA MUTULA, Bowerbank. 

 Plate LXXIV. 



Sponge sessile, massive. Surface openly reticulated. 



14 



