290 PLATE LXXXt. 



and slender. Interstitial membranes thin and delicate, 

 aspiculous. 



Colour. — In the dried state, light gray. 



Habitat. — Plymouth ; Mr. C. Stewart. 



Examined. — In the dried state. 



I am indebted to my friend the Rev. A. M. Norman, 

 for my knowledge of this sjoecies which he obtained, 

 with other sponges from Plymouth, of Mr. C 

 Stewart. 



This sponge covers and closely embraces the stems 

 of a slender zoophyte for two and a quarter inches of 

 its length. It does not envelop the whole into one 

 mass ; but it assumes the form of a branching sponge, 

 the branches being about three lines in diameter with 

 two or three smaller ones thrown off laterally. It is ex- 

 tremely tender and fragile in structure. The primary 

 lines of the skeleton run in the direction of the long axes 

 of the sponge, and this is their normal course in a branch- 

 ing species; in other species of Isodictya, where the',habit 

 is more decidedly parasitical, they are often based on 

 the body on which they are located and their direction 

 is then from the centre to the circumference of the 

 mass ; so that it would appear that the sponge under 

 consideration was normally a branching species. Very 

 few of the oscula could be detected in consequence of 

 nearly the whole of the dermal membrane being absent. 

 The few patches of the dermal membrane remaining 

 were thin and pellucid and apparently aspiculous. The 

 skeleton rete is very open audcavernulous. The primary 

 lines, rather distant from each other, meander in a very 

 tortuous mode in a longitudinal direction, and this 

 necessarily produces great irregularity in the dis- 

 position of the secondary lines of the skeleton, but 

 although irregular to this extent, the normal structural 

 peculiarities of an Isodictya are unmistakably apparent. 

 The spicula of the primary hues of the skeleton are 

 rather larger and stouter than those of the secoudarj^ 

 ones ; but the whole of them are small and very slender. 

 One of the largest of them measured -r\-^ inch in 



