458 DR. J. s. BOWERBANK ON [June 5, 



they are not so abundantly furnished with tension-spicula, while the 

 retentive ones are the same in form and about the same ia number. 

 These organs are not very readily detected in situ while immersed in 

 the sarcode ; and from the delicacy of their structure they require a 

 microscopical power of at least xthjU linear to render them distinctly 

 to the eye. 



The gemmules of the sponge are rather numerous on the inter- 

 stitial membranes, and on the inner surface of the dermal one. They 

 are smooth, spherical or slightly oval, and opaque and black, whe- 

 ther viewed by direct day-light, or, when mounted in Canada balsam, 

 by transmitted light. They vary to some extent in size : the smallest 

 of them measured ^ihro ^^'^^ "^ diameter, the largest Ysto inch; but 

 the average of several measured was -j-sW '•^ch in diameter. 



2. ISODICTYA ASPERA, Sp. nOV. 



Sponge sessile, multifistulous, fistulae branching irregularly and 

 usually confluent ; parietes thick ; surface very rough and irregular. 

 Oscula within the fistulse. Pores inconspicuous. Dermal mem- 

 brane spiculous, reticulated ; rete irregular, uni- or bispiculous ; 

 spicula acuate, same size as those of the skeleton. Skeleton : Rete 

 irregular, diffused ; primary fibres multispiculous, secondary fibres 

 irregularly disposed ;^ acuate, stout and rather long. Gemmules 

 membranous, abundant, more or less congregated, spherical, semi- 

 transparent, dark amber-colour. 



Colour. In the dried state, dark brown. 



Hab. Abu, Philippine Islands (Dr. A. B. Meyer). 



Examined in the dried state. 



Type in the Dresden Museum. 



This sponge rather exceeds six inches in height, and is of about 

 the same average diameter. 



The fistulse radiate in all directions from the massive basal attach- 

 ment, and immediately separate more or less into short stout 

 branches which most frequently become confluent groups. This 

 character of the fistulse is very unusual, and is very characteristic of 

 the species. The surfaces of the fistulse are exceedingly rough and 

 rugged ; and their substance is very brittle in the dried state. Their 

 distal terminations are open to the full extent of their internal 

 diameters ; and their margins are thin. The oscula on the smooth 

 inner surfaces of these organs are distinctly visible by the aid of 

 a lens of about two inches focus. 



Portions of the dermal membrane, when mounted in Canada bal- 

 sam ; and viewed with a linear power of about 100, exhibit its reti- 

 cular structure in a very satisfactory manner ; the rete is rather 

 irregular, but very distinctly exhibited ; it is most frequently uni- 

 spiculous ; but occasionally two or, rarely, three spicula are combined 

 in some parts of it. The spicula are nearlj equal in size and of one 

 form only, rather long and stout acuate. In a portion of the dermal 

 membrane thus examined, there were a considerable number of 

 groups of gemmules, each group consisting of numerous closely 



