462 DR. J. S. BOWERBANK ON THE SPONGILLID^. [NoV. 24, 



form of spiculum was associated with them in this fragment of an 

 ovarium ; nor could I by the most careful examination of the frag- 

 ments of the Sponge in my possession detect any other remains of 

 the ovaria. Among the spicula separated by incineration, I found a 

 single acuate spiculum of the following dimensions : — length -^^ inch, 

 diameter 2TjVu inch. These proportions are very nearly in accord- 

 ance with those of the skeleton-spicula, and it is very probable that 

 it has belonged to the case of one of the gemmules of this Sponge, 

 especially as it is different from the spicula belonging to any of the 

 known species of Spo7igilla from the River Amazon. 



A portion of the sarcode still remains in the Sponge ; and when 

 expanded in water, it has a golden-yellow colour, and has a dense ge- 

 latinoid appearance. 



Spongilla lacustris, Johnston, 



Ephydatin canalium, Fleming. 

 Halichondria lacustris, Fleming. 



Sponge sessile, branching ; surface more or less hispid. Oscula 

 simple, dispersed, small, and numerous. Pores inconspicuous. 

 Dermal and interstitial membranes pellucid, spiculous ; spicula nu- 

 merous, fusiformi-acerate, entirely spined ; spines abundant, conical, 

 acute. Skeleton-spicula subfusiformi-acerate. Ovaria subglobose ; 

 spicula acerate, much and variably curved, disposed at right angles 

 to lines radiating from the centre of the ovaries, entirely spined ; 

 spines conical, acute. 



Colour dark green. 



Hab. Lakes and rivers of England and Scotland. 



Much uncertainty has existed regarding the specific distinctions 

 belonging to the two well-known European species of Spongilla ; and 

 1 can only attribute this indecision on the part of naturalists to their 

 having hitherto appealed to the characters of external form and sub- 

 stance as a means of discrimination, to the almost total exclusion of 

 those of internal structure, in which may be found striking and un- 

 failing specific differences which never vary under any circumstances 

 of locality or modification of external form. 



Dr. Fleming has justly characterized this species as being "massive, 

 rising into short rounded branches ; the fibres are coarser and the 

 substance denser than those of S.Jluviatilis ; the spicula, too, though 

 similar in form, are thicker and about one- fourth shorter." This de- 

 scription, when both species are attainable, is good as regards the 

 differential characters ; but fortunately there are essential characters 

 of much higher value, which exist in the spicula of the dermal mem- 

 brane and in those of the ovaria, neither of which have, I believe, 

 been noticed by previous writers on these subjects. Those of the 

 dermal membrane are, under ordinary circumstances, very indistinct. 

 If we examine the membrane in water between glasses, the spicula, 

 as they lie immersed in the sarcode, are scarcely to be detected ; but 

 if previously mounted in Canada balsam, they become at once di- 

 stinctly visible ; they are very numerous, and are disposed over the 



