276 PLATE LXXXIII. 



in length, very numerous, rather short, entirely spined; 

 spines large and strong. Interstitial membranes 

 abundantly spiculous ; tension spicula same as those of 

 the skeleton, intermixed with internal defensive spi- 

 cula ; retentive spicula same as those of the dermal 

 membrane. 



Colour. Dried, brown, with a tint of yellow. 



Habitat. Polperro ; Mr. Jonathan Couch. Fowey 

 Harbour ; Mr. C. "W. Peach. 



Examined. In the dried state. 



This sponge, for which I am indebted to Mr. Couch, 

 is an elongately ovoid mass one and three quarters of 

 an inch in length and nearly an inch at its greatest 

 diameter. It has apparently been parasitical on a 

 fucus or zoophyte, the remains of which are to be seen 

 at the largest end. The surface is pustulous, the eleva- 

 tions are usually flat at their apices ; occasionally an 

 osculum appears on their summits ; but more frequently 

 these organs are situated in the spaces between them. 



In these external characters this species very closely 

 resembles If. fictitia, and its internal organs are also 

 in form nearly like those of that species ; but although 

 thus far agreeing in form their proportions are so dis- 

 tinctly different as to render their separation as species 

 in a perfectly satisfactory manner. The dermal mem- 

 branes of both species are about equally abundantly 

 supplied with tension spicula, and they also agree very 

 closely in their mode of disposition ; but in the propor- 

 tions of their length and diameter they vary exceedingly, 

 the spicula of M. fraudator not being more than half 

 the length of those of M. fictitia, while they are quite 

 equal to them in diameter. The form of those of the 

 latter species are purely acerate, while in the former 

 they are distinctly fusif ormi-acuate. Similar differences 

 exist in the retentive spicula of the dermal and inter- 

 stitial membranes of the respective species ; those of 

 M. fictitia being at least twice as stout as those of 

 M. fraudator. 



The like discrepancies also obtain in their internal 



