60 A MONOGRAPH OF THE 



gillum. This species and others nearly allied to it in the 

 Museum of the Jardin des Plantes, at Paris, designated 

 Alcyoncellum corbula, each, like the sponge under considera- 

 tion, consists of a single, large fistula, without any promi- 

 nent basal mass, but is simply cemented at, or near its 

 basal extremity to any foreign body against which it may 

 happen to press during its growth. 



The dermal membrane is translucent, but comparatively 

 stout, and the external defensive spicula are irregularly 

 dispersed on all parts of it, their bases being cemented on 

 its outer surface, without any apparent reference to the 

 secondary lines of the skeleton immediately beneath them, 

 and they radiate from the surface in every possible direc- 

 tion. From the structure of the network of the skeleton 

 of the external surface of the sponge, it naturally results 

 that the pores are congregated in the areas of the large 

 reticulations, and within their spaces one or two open pores 

 were occasionally observed, but in the specimens under 

 consideration they were of rather rare occurrence. In the 

 dried specimen, the inhalent areas are depressed to the 

 extent of more than the length of a defensive spiculum, 

 and it is probable that this depression existed to a certain 

 extent in the living state. In a fragment of a specimen 

 of this species, sent to me by Mr. Bailee, and consisting 

 of the extreme apex of the sponge, there are no indications 

 of compression or collapse, the terminal portion being 

 hemispherical, exhibiting a series of areas strongly indica- 

 tive of a congregation of oscula, and very unlike those of 

 the parietes of the general mass of the sponge. 



The primary lines of the skeleton are situated at the 

 inner surface of the sponge. They are rather distant from 

 each other, and there are frequently more than one series 

 of interstitial spaces intervening between them. The 

 thickness between the outer and inner surfaces of the 

 sponge is greater than that in P. mammillaris, and almost 

 equal to that of P. robusta, although the general aspect of 

 the sponge is more transparent, and apparently fragile than 

 either of the fistular portions of those species. 



