1873.] DR. J. S. BOWERBANK ON THE SPONGIAD.E. 321 



beneath, through the spaces between the apices of the conical organs. 

 When the inner surface of this group of radiating organs is examined, 

 the basal aperture of each is usually found to be completely open ; 

 but in some cases, as represented in one of them at a, fig. 8, there is 

 what appears to be the remains of a closing membrane ; it is, however, 

 only in a very few cases that I have observed the remains of such 

 an organ. 



These singular radial organs are not present on the distal end of 

 the sponge for about two inches of its length ; and I examined this 

 portion of it carefully in search of pores. I found the dermal mem- 

 brane in a better state of preservation than on its proximal end, and 

 its reticular structure well demonstrated. A few isolated pores in an 

 open condition appeared at distant intervals ; but many of these had 

 more the aspect of orifices, by contraction of the membrane in dry- 

 ing, than of well-defined pores. I did not find any pores open in 

 the pocilla beneath the radial coverings ; but this is not surprising. 

 as in dead sponges the general rule is to find them closed, and the 

 exception is to find them open. 



The gemmules are not numerous. I found one only in the section 

 at right angles to the surface of the pocillum represented by figure 7 ; 

 but in other cups taken from close to the proximal end of the 

 sponge there were considerable numbers of them disposed on the 

 inner surface of the membrane, and on the outer surfaces of the 

 sacculi of the disk there were a few attached to those surfaces ; but 

 none were found within any of the conical sacculi, although their 

 open mouths within the pocilla might have led us to expect 

 to see some of them there. The gemmules are membranous, 

 round or oval, semitransparent, and of a dark amber-colour, just 

 such as we find in numerous other species of Isodictya. I searched 

 in vain for them in the surrounding skeleton-tissues ; but I found 

 solitary ones only at distant intervals attached to the reticulations of 

 more distant parts of the skeleton. 



Since the above description was written, on looking over a collection 

 of sponges I purchased of the late Mr. James de Carl Sowerby many 

 years since, I found another specimen of the species. It is similar 

 in form to the figured one, is an inch shorter, and has neither its 

 natural base nor its apex, but is rather larger in its diameter. Its 

 inhalant and exhalant organs are exceedingly like those of the type 

 specimen ; but the latter are rather large. In their anatomical 

 characters, the two specimens are in perfect accordance. 



Dictyocylindrus dentatus, Bowerbank. (Plate XXIX.) 

 Sponge ramose, pedicelled, pedicel short and stout ; branches very 

 numerous, ascending, culminating towards the apex of the sponge, 

 occasionally dividing or inosculating, furnished abundantly with 

 stout tooth-shaped processes. Surface smooth. Oscula simple, 

 minute. Pores inconspicuous. Dermal membrane coriaceous, pro- 

 fusely furnished with dentato-cylindro-hexradiate retentive and de- 

 fensive spicula ; radii very short and stout ; apices bi- or tridentate. 

 Skeleton — spicula acnate, long and rather stout, and rarely cylin- 

 Proc. Zool. Soc— 1873, No. XXI. 21 



