98 A MONOGRAPH OF THE 



is an indication of a natural tendency to locomotion belong- 

 ing to the adult species that I have ever observed among 

 the Spongiadse. 



The oscula were most numerous and largest near the 

 margin of the under surface, and a few only were apparent 

 on the upper surface of the smaller specimen. 



The greater number of the pores were closed ; a few 

 thiat were open on the upper surface of the larger specimen 

 were very minute when viewed with a power of one hun- 

 dred linear by direct light. 



The dermal membrane on both surfaces is crowded with 

 its peculiar spicula. They are singular in their form, being 

 fusiformi-acerate, not curved as is usually the case with 

 such spicula, but bent abruptly near the middle of the 

 shaft, so as to form more or less of an angle, and at or 

 near this spot there is generally an inflation of the shaft. 

 The adult spicula are profusely and entirely spinous, but 

 when not fully developed they are frequently quite smooth, 

 or have the spines but very faintly indicated, but although 

 not fully developed they are rarely without the inflation at 

 or near the angle. 



The skeleton spicula are remarkably large and very 

 variable in form and proportions. The large, long, spinu- 

 late form, with one or two extra inflations, near the base 

 of the shaft, are all disposed in one thin stratum, about 

 midway between the upper and lower surfaces of the 

 sponge, the bases being all towards the centre, and 

 their points radiating towards the circumference. The 

 short, stout, attenuato-spinulate and fusiformi-spinulate 

 ones, with occasionally one extra inflation near the base, 

 are mixed together, without order, in a thick stratum, which 

 occupies the space between the stratum of long spinulate 

 spicula and the lower surface of the sponge. The interval 

 between the central stratum and the upper surface is 

 occupied by large cavernous spaces which communicate by 

 orifices in the interstitial membranes, which, are abun- 

 dantly furnished with tension spicula dispersed on their 

 surfaces. Numerous hollow, irregular ridges or cones of 

 dermal membrane are projected from the upper surface of 



