150 A MONOGRAPH OF THE 



dition. The surface in the dried state has a few of the 

 longest of the internal defensive spicula with their apices 

 projecting through the dermal membrane, but this, I appre- 

 hend, is due to the contraction of the sponge in drying. 

 The oscula are minute, and are only visible by the aid of 

 an inch lens. The dermal membraue, strictly speaking, is 

 aspiculous, as there are no tension or retentive spicula 

 appropriated either to it or to the interstitial membranes ; 

 but the large and widely-spreading groups of skeleton 

 spicula are occasionally based on its inner sm-face, and 

 thence radiate into the body of the sponge. But by far 

 the greater number of these radiating groups are based on 

 the basal or the interstitial membranes ; the spicula of the 

 skeleton require a linear power of about 400 to render 

 their form distinct. Their bases are irregularly crowded 

 together, while their shafts are projected outward at every 

 imaginable variety of angle. The supplementary large 

 acuate or sub-clavated acuate spicula are a singular appen- 

 dage to the skeleton ; they are of extreme length, and more 

 than twice the largest diameter of the spicula of the radial 

 groups, and are disposed in lines parallel to the basal 

 membrane ; they are usually disposed singly, but occasionally 

 two occur together, or very closely so. The internal 

 defensive spicula are very numerous, and appear all to 

 spring from the basal membrane, their diameter is nearly 

 the same at the base, but they vary greatly in their length 

 and also in the degree of their spinations; in some the 

 spines are quite in an incipient state, while in others they 

 are well and distinctly produced. 



2. Hymedesmia stellata, Bowerbank. 



Sponge. Coating very thin ; surface even, hispid. Oscula 

 simple, dispersed, minute. Pores inconspicuous. 

 Dermal and basal membranes abundantly spiculous; 

 spicula cylindro-stellate, very minute. Skeleton : 

 spicula ovo-spinulate, very large and long, variable in 

 size, closely fasciculated, bases and apices concurrent. 



