1874.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 299 



multiangulated cylindrical retentive spicula ; they are so minute as 

 to require a power of five or six hundred linear to render their 

 forms distinctly to the eye. The number of angles in these spicula 

 vary from two or three to six or seven ; and in some cases the angu- 

 lation is very distinctly and regularly produced. 



From the thin coating nature of the sponge the skeleton-arrange- 

 ment is not so readily demonstrable as in many other species of the 

 genus. The fasciculi are abundantly spiculous and very compactly 

 constructed. The bases of the spicula are all coincident and 

 proximal, while all the apices are distal as regards the direction of 

 the fasciculi. 



The interstitial membranes are in many parts literally crowded 

 with the arborescent elongo-subsphero-stellate retentive spicula, and 

 they are also dispersed in considerable quantities amongst the ovaria 

 in the dermal crust. These spicula are singular and very character- 

 istic organs. The specimen figured is a very fully developed one. 

 They vary in degree of development to a very considerable extent ; 

 and in some the central mass is very thin and elongate. 



In the dermal crust of the sponge none but fully developed ovaria 

 are to be found ; but they are dispersed in considerable numbers on 

 all parts of the interstitial membranes, and in every stage of 

 development from an elongately oval loosely aggregated mass of 

 very minute spicula to the compact and fully matured organ. The 

 spiculous structure of these ovaria is very much finer and more 

 minute than in any other species of Geodia with which I am ac- 

 quainted. 



Geodia imperfecta, Bowerbank. (Plate XLVI. figs. 6-13.) 



Sponge massive, tuberous, sessile. Surface smooth. Oscula 

 simple, minute, dispersed. Pores inconspicuous. Dermal mem- 

 brane unknown. Skeleton — fasciculi rather loosely constructed ; 

 spicula subfusiformi-acerate, rather stout and short. Connecting 

 spicula attenuato-patento-ternate ; radii rarely perfectly developed, 

 distal terminations recurved, not very numerous. Interstitial mem- 

 branes — retentive spicula sphero-stellate with cylindro-subfoliate 

 radii, numerous ; and attenuato-stellate, variable in form, occasionally 

 subsphero-stellate more or less. Ovaria oval, depressed. 



Colour in the dried state cream-white. 

 Hab. South sea. 

 Examined in the dried state. 



I obtained four specimens of this species from a dealer in objects 

 of natural history ; they are each attached to the basal portion of a 

 specimen of Oeulina rosea from the South Sea ; the figured specimen 

 is the largest of the four. The whole of them possess the same 

 description of tuberous massive form ; the smallest two did not 

 exceed an inch in length by about half an inch in breadth. The 

 oscula are so small as to require the aid of a lens of two inches focus 

 to render them readily apparent. I could not find any remains of 

 the dermal membrane on either of the specimens. The connecting- 



20* 



