PLATE LXXJ. 183 



mounted in Canada balsam or on the general mass of 

 the sponge. 



The dermal membrane is aspiculous closely enve- 

 loping the mass of the sponge. 



The whole substance of the sponge is composed of a 

 loosely and irregularly disposed stratum of spicula, 

 lying to a great extent in the same plain, but crossing 

 each other in every imaginable direction. The spicula 

 are of nearly the same size, and of but one form, all 

 being more or less spinulate. In some of them the 

 spinulation is fully and completely developed, while in 

 others it is quite in an incipient condition, and every 

 gradation of development between the two extremes 

 may be observed. 



The interstitial membranes are very translucent, 

 and without the assistance of the minute molecules of 

 extraneous matters upon them would scarcely have 

 been detected. 



DESMACIDON CONSTKICTUS, BowerbanJc. 



Vol. ii, p. 350, ' Mon. Brit. Spongiadse.' 



I have unfortunately mislaid the type-specimen of 

 this species described in vol. ii, p. 350, ' Mon. Brit. 

 Sponges,' but a figure of it is, in truth, but of little 

 consequence in regard to its future recognition, as its 

 structural peculiarities are so strongly marked as to 

 render its discrimination an easy task. 



A re-examination of some minute fragments of it has 

 produced two forms of retentive spicula that I had not 

 seen in the previously examined portions of the spe- 

 cimen. I found in one mounting of the spicula seven 

 specimens of the small dentato-palmate inequi-ancho- 

 rate form represented by fig. 7, Plate LXXI, all 

 agreeing in size and proportions ; two of the large 

 description of dentato-palmate inequi-anchorate ones 

 represented by fig. 8, and one large bidentate inequi- 

 anchorate spiculum represented by fig. 9. 



