204 PLATE LXX1II. 



tension spicula acerate, minute, and very slender, few 

 in number ; retentive spicula simple and contort, 

 bihamate, minute and slender, not very numerous. 

 Skeleton. Reticulations regular and distinct, rete 

 rarely more than unispiculous ; spicula acerate, rather 

 stout. Interstitial membranes pellucid, spiculous ; 

 tension and retentive spicula same as those of the 

 dermal membrane, few in number. 



Colour. Dried, light gray. 



Habitat. Coast of Cornwall ; Mr. Jonathan Couch. 



Examined. In the dried state. 



I am indebted to Mr. Jonathan Couch for my 

 knowledge of this species. The specimen is half an 

 inch in height, three lines in breadth, and about half a 

 line in thickness, and is of an elongo-ovate shape, the 

 basal extremity being the largest end. The oscula 

 are very small and scarcely visible without the aid of a 

 lens of about half an inch focus. 



The reticulations of the dermal membrane are coin- 

 cident with those of the skeleton beneath. The 

 tension and retentive spicula are very few in number 

 and so minute as to require a power of 400 linear to 

 define them accurately. The structural characters of 

 this species, as regards the skeleton, are very similar 

 to those of the corresponding parts of Halichondria 

 angulata, but the spicula of the latter are longer in the 

 proportion of about three to two than those of the 

 former, and they are also more slender in their pro- 

 portions ; but on a minute examination the presence of 

 the bihamate spicula and the total absence of the sub- 

 angulated tricurvate acerate tension spicula of E. 

 angulata readily separate the two species. 



MTCROCIONA SIMPLICIMA, Bowerbmk, 

 Plate LXXIII. 



Sponge coating, surface irregular. Oscula simple, 

 dispersed. Pores inconspicuous. Dermal membrane 



