HYMENIACIDON. *17 



two Indies in length, one in breadth, and one in height, 

 and incorporated in it are several small pebbles, 

 and a small branching specimen of NulUpora poly- 

 morpha. From about the middle of the mass there 

 rises an irregular stick-like branch three inches in 

 height, rather exceeding half an inch in diameter. The 

 surface is slightly corrugated in its present condition, 

 but this is evidently the result of drying. The oscula 

 are small and not very readily detected, excepting a 

 few rather larger than the rest, upon the basal por- 

 tion of the sponge. The most striking distinctive 

 characters are those of the dermis, the form and 

 mode of the reticulation of which differs essentially 

 from that of its nearest allies. The rete is very 

 irregular, and the areas very angular in consequence 

 of its being constructed of numerous fasciculi of rather 

 large and long spicula, which vary in number from two 

 to four or five in each fasciculus ; and also from the 

 fasciculi being disposed on the membrane in a very 

 irregular manner, crossing each other at a variety of 

 angles ; the spicula, unlike those of the skeleton, are 

 all large and uniform in size, while those of the skeleton- 

 tissues are very variable in their diameters, and very 

 few of them equal in size and robustness to those of 

 the dermis. 



" The only two known British species with which this 

 sponge might possibly be confounded are Eymenia- 

 cidon reticulatus and R. tegeticula. The dermal mem- 

 brane of H. reticulatus differs considerably from that 

 of H. solidus, inasmuch as it is more regularly reticu- 

 lated ; the rete is stronger and multispiculous, and the 

 areas more regularly produced ; and the spicula, 

 although of the same form as those of E. solidus, are 



