72 A MONOGRAPH OF THE 



extremities are often expanded laterally to the extent of half 

 as much more as the average width of the tube. I am 

 also indebted to the Rev. A. M. Norman, for the examina- 

 tion of a specimen of this sponge, which was dredged up 

 on the coast of Guernsey, in the autumn of 1859. It is 

 attached to a piece of an old oyster shell. It is irregularly 

 conical in form, an inch and three-quarters in diameter at 

 the base, and its greatest height seven lines. The hispid 

 character of the surface is visible to the unassisted eye. 

 There was one or two simple oscula, probably due to the 

 destruction of as many fistulas while alive, the largest not 

 exceeding half a line in diameter, the remainder of them, 

 about sixteen in number, were all more or less mammseform, 

 but apparently not in a fully developed condition, the tallest 

 of them not exceeding two lines in height, and the greater 

 portion were in a closely collapsed state. The fasciculi of 

 skeleton spicula running longitudinally from base to apex 

 of these cloacal appendages, do not appear to deviate from 

 a straight line. The primary external defensive spicula of 

 the basal mass of the sponge are continuations of the fasci- 

 culi of the skeleton, but the secondary series of external 

 defensive spicula of the same mass have their bases beneath 

 the dermal membrane, through which, in the dried state, 

 they are projected for about one third of their length, and 

 as they are exceedingly numerous, their presence gives a 

 sub-crustular character to that portion of the dermal struc- 

 ture. This sub-crustular texture does not exist in the 

 cloacal fistulse. In these portions of the sponge there are 

 no primary defensive spicula, but their surfaces are abun- 

 dantly furnished with secondary defensive spicula, which 

 are based on the external surface of the dermal membrane. 

 They are mostly collected into radiating fasciculi, imme- 

 diately above the transverse fasciculi of the skeleton, but a 

 ^exv of them spring singly from the surface of the dermal 

 membrane in the spaces between the skeleton fasciculi. 

 On many of the cloacal fistulas they were so numerous as 

 to render it very difficult to determine correctly their true 

 positions. 



The tension spicula of the interstitial membranes are of 



