336 A MONOGRAPH OF THE 



42. Isodictya lurida, Bowerbank. 



Sponge. Massive, sessile. Surface even, smooth. Oscula 

 simple, dispersed, small and numerous. Pores in- 

 conspicuous. Dermal membrane abundantly spicu- 

 lous ; tension spicula cylindrical, occasionally sub- 

 clavate, mucronate, or hastate ; disposed sometimes in 

 flat radiating groups, at others, parallel, in broad 

 fasciculi ; and also slender long acuate spicula, entirely 

 spined, dispersed; retentive spicula bidentate equi- 

 anchorate ; dentes very long, shaft slender. Skeleton 

 very diffuse and open ; primary lines multispiculous, 

 sinuous and irregular ; secondary lines irregular, 

 rarely more than bispiculous. Spicula sub-fusiformi- 

 acuate, basally and apically spined ; spines few in 

 number, minute. Interstitial membranes. Tension 

 spicula acuate, very slender, sometimes flexuous, few 

 in number; retentive spicula same as those of the 

 dermal membrane ; unequally distributed, sometimes 

 numerous, dispersed, at other times entirely absent. 



Colour. Dried, dark nut-brown. 



Habitat. Three miles off Dunstanborough, Northum- 

 berland, Rev. A. M. Norman. 

 Examined. In the dried state. 



The specimen is irregularly massive, two inches in 

 length, and one and half in width, and its greatest height is 

 three fourths of an inch. 



The dermal tissues of this sponge are very characteristic 

 of the species ; the abundant groups of radiating tension 

 spicula, with the occasional occurrence of parallel bundles, 

 render it unlike any other nearly allied species with which 

 I am acquainted. The tension spicula of the dermal 

 membrane are nearly equal in their length and diameter ; 

 but their terminations are subject to much variation in 

 form, no two scarcely being alike in that respect. The 



