HALICHONDRIA. 103 



lated; spicula acerate, short and stout. Interstitial 

 membranes aspictdous. 



" Colour. — In the dried state, dull ochreous yellow. 



" Habitat. — Isle of Man ; Mr. D. Eobertson. 



^'Examined. — In the dried state. 



" This sponge was presented to my friend the Rev. A. 

 M. Norman by Mr. D. Robertson, and was sent to me 

 for examination. It is an irregularly branching, com- 

 pressed mass, four inches in height and about half an 

 inch in width, the oscula on low tubercles being 

 disposed on the margins of the mass. The dermal 

 membrane, mounted in Canada balsam, and viewed 

 with a power of TOO linear, is a very characteristic 

 object ; the rete is monospiculou«, and never appears 

 to exceed the length of one spiculum wide, and the 

 areas very rarely assume any other form than that of 

 a triangle; occasionally a quadrangular one may be 

 observed, but this is the exception and not the rule. 

 The mode of the disposition of the triangidar areas is 

 very irregular, but very characteristic of the species. 

 The peculiar structure of the skeleton is very remark- 

 able. The rete is very close and complicated ; it is 

 composed of numerous multispiculous fasciculi of short 

 acerate spicula, so closely and densely packed together 

 as to render the regular reticulated structure of the 

 skeleton in some parts very indistinctly, and amid this 

 mass interstitial cavities are irregularly distributed. 



" The intermarginal cavities in this sponge are very 

 distinctly and beautifully developed, and are very 

 interesting objects in a slice of the sponge at right 

 angles to the dermal surface when mounted in Canada 

 balsam, with their beautiful canopy of reticulated 

 dermal tissue. 



