1863.] DR. J. S. BOWERBANK ON THE SPONGILLIDjE. 469 



but present a sharp membranous margin level with the adjoining 

 surface. 



The spicula of the dermal membrane are not very numerous ; they 

 are slightly curved, and are entirely and abundantly spinous ; and the 

 spines are not in an incipient state, as on those of the skeleton, but 

 are fully and distinctly produced ; their spinous character is not 

 usually distinctly apparent while in situ, in consequence of the den- 

 sity and colour of the sarcode and the abundance of the molecules 

 imbedded in it ; but when separated, there can be no mistake re- 

 garding them. These spicula are also found imbedded in the inter- 

 stitial membranes, but they are comparatively rare in those tissues. 



The incipient spines of the spicula of the skeleton are few and mi- 

 nute, and require a power of about 400 linear to render them di- 

 stinct to the eye, and, unless it be on large and fully developed 

 spicula, they are frequently indicated only by a slight elevation of 

 the profile lines of the spicula. 



Although in some points of organization this species is the repre- 

 sentative in India of our European S. lacustris, there is no simi- 

 larity whatever in external form : while S. lacustris is always arbo- 

 rescent, the Indian one is always sessile and coating, rarely attaining 

 an altitude exceeding an inch. In <§. lacustris the skeleton-spicula 

 are acerat«, of nearly the same diameter for the greater portion of 

 their length ; while in /S. cinerea they are distinctly fusiformi-acerate, 

 gradually attenuating from the middle of the shaft towards each end; 

 they are also larger and have a greater length than those of S. la- 

 custris, measuring ^L- inch long, while the latter is but -^ inch long, 

 and are entirely destitute of incipient spines. 



In the size of the ovaries of the two species the proportional dia- 

 meters are the reverse of the measurements of the skeleton-spicula. 

 The largest ovary is that of S. lacustris, ^jL inch in diameter, while 

 that of S. cinerea is but -^ inch in diameter. 



The mode of disposition and the form of the dermal spicula of the 

 gemmules of the two species is very similar: they are each abundantly 

 spinous and variable in size ; but those of S. cinerea are all only 

 slightly curved, while those of S. lacustris are frequently curved to 

 so great an extent as to form a semicircle. In length they are as 

 nearly as possible equal ; but in S. lacustris they have a diameter 

 twice as great as those of S. cinerea, the average diameter of the 

 latter being ygVir inch, while that of the former is ^bV? inch, 



Spongilla Carteri, Bowerbank. 



<S. friabilis. Carter. 



Sponge sessile, massive ; surface even. Oscula numerous, di- 

 spersed. Pores conspicuous. Dermal and interstitial membranes 

 thin, pellucid, aspiculous. Skeleton-spicula fusiformi-acerate, stout. 

 Ovaries subglobose; spicula fusiformi-acerate, disposed at right angles 

 to lines radiating from the centre.of the ovary, short, and stout. 



Colour bright green. 



Hub. Freshwater tanks, Bombay {Carter). 



Examined in the dried state. 



