DESMACIDON. 175 



diameter ; and the basal constriction, so characteristic 

 of the skeleton spicula, is also present, but not so 

 strikingly marked as in the larger ones of the 

 skeleton fibres. The simple and contort bihamate 

 retentive spicula are dispersed abundantly among the 

 tension ones, and among them there are sparingly 

 dispersed very minute inequi-bidentate anchorates, 

 and a few inequi-dentato-palmates. The lengths of 

 the latter two forms average the TlVsth inch, while 

 the length of the bihamates varied from ^-^th mcn 

 to g^th inch ; and a very few minute and slender 

 tricurvate, acerate tension spicula were dispersed among 

 them. 



" The oscula are small, simple, round or oval orifices 

 dispersed on the surface of the sponge, and are not 

 readily detected without the aid of a lens of two inches 

 focus. 



"In a specimen of the dermal membrane mounted 

 in Canada balsam a few pores in an open condition 

 were seen. 



" The interstitial membranes were abundantly spicu- 

 lous, but not to such an extent as the dermal, and 

 the mode of disposition of the tension spicula was 

 somewhat different, as in many parts they were more 

 or less fasciculated, the fasciculi being disposed at 

 about right angles to the longitudinal fibres, between 

 which they were situated. These membranes were 

 furnished with the same descriptions of retentive 

 spicula as those of the dermal membrane. 



" The additional information obtained from the ex- 

 amination of the structures of the specimen described 

 above, enables me to render the description of its 

 specific characters much more complete, and I pro- 



