330 DR. J. S. BOWERBANK ON THE SPONGIAD^. [Mar. 18, 



by a thick layer of indurated sarcode. The distal ends of these 

 organs are protected by an irregular fringe of small fusiformi-sub- 

 acuate or acerate external defensive spicula. These conditions of the 

 dermal crust and the iutermarginal cavities unmistakably indicate 

 the congregation of the pores on the dermal membrane. 



The oscula are few in number ; they are congregated in a slightly 

 depressed area ; the largest does not exceed the tenth of an inch in 

 diameter. The connecting-spicula are comparatively small and few 

 in number ; they do not penetrate the dermal crust, but their 

 ternate terminations are closely applied to the proximal surface of 

 the stratum of indurated sarcode immediately beneath the dermal 

 crust. The greater portion of them are subexpando-ternate ; but 

 some of them are nearly patento-ternate. They vary in length from 

 about 3^ to ^ inch. The fusiformi-acerate spicula of the skeleton 

 are very numerous ; they average -^ inch in length, while the fusi- 

 formi-acerate tension ones, which are abundantly intermixed with 

 them, seldom exceed y^ inch in length. 



The two forms of cylindro-stellate retentive spicula differ con- 

 siderably in size. Two of them, imbedded closely adjoining each 

 other in the interstitial membranes, measured from the distal 

 extremities of their opposite radii as follows : — the largest one ytti 

 inch extreme diameter, the minute cylindro-stellate form ^-gVff inch 

 extreme diameter, while the radii in each were nearly of the same 

 diameter. They do not appear to pass into each other by variations 

 in the proportional length of the radii, but each variety seems to 

 adhere to nearly the same dimensions ; neither do they appear to 

 occupy particular positions on the tissues, but are irregularly dis- 

 persed over the interstitial membranes. 



The adult ovaries are perfectly globular, or very slightly depressed 

 at the foramen ; they measure - 4 ^-j inch in diameter ; the cunei- 

 form spicula of which they are composed are comparatively large, 

 and the distal extremities are strongly developed and are very 

 angular. Ovaria in all stages of development were present in 

 abundance in all parts of the interior of the sponge. The structural 

 peculiarities of the ovaries in this species are more than usually 

 beautiful when viewed with a power of about 700 linear. The 

 distal termination of each spiculum in the adult specimens presents 

 an acutely angulated stellate appearance, closely resembling a five- or 

 six-rayed star, the radii of which are acutely conical, cemented together 

 by translucent silex, so that each ovarium resembles a beautiful crystal 

 sphere, regularly ornamented with innumerable minute Stellas. 



Many years have passed since I first examined this sponge, but I 

 have never been fortunate enough to meet with another specimen. 



Tethea hispida, Bowerbank. (Plate XXXI.) 



Sponge sessile (?) ; surface strongly and thickly hispid. Oscula 

 and pores inconspicuous? Dermis abundantly spiculous ; spicula 

 disposed at right angles to the surface, uniformly crowded together; 

 superfusiformi-subovo-spinulate, very minute, forming a secondary 

 series of defensive spicula. Primary series of defensive spicula super- 



