Species of HexactinelUd Sponge. 277 



diminished form, which soon expands into a flat portion that 

 terminates in the double hook, — the double hook being com- 

 pressed and crescentic in the smooth form, and twice the 

 breadth of that in the spiniferous ones, where, on the other 

 hand, the body is a little thicker and the hooks a little more 

 recurved, still always opposite. 3. The minute surface-spicule 

 is also nail-like, and consists of a bushy plumose shaft fur- 

 nished with four rays parting from the fixed end of the former 

 at right angles, and directed a little forwards or away from 

 the shaft, cup-like, — the plumose appearance of the shaft 

 arising from the presence of a number of long spines, which, 

 originating all round it, are inclined towards its free or 

 pointed extremity ; while the arms are equally spined, but 

 with short conical eminences, especially towards their abruptly 

 pointed extremities : among these spicules there are also two 

 kinds, viz. one thick, short, and stout, and the other com- 

 paratively long and slender, with the shaft slightly curved or 

 turned to one side. 4. The birotulate spicule, consisting of a 

 straight shaft, sparsely spinous in the centre, and expanding 

 at each end into eight blades or arms, which are altogether 

 recurved dome-like towards the centre of the shaft. 5. A 

 minute hexaradiate spicule, the arms of which are equal, 

 opposite, and furnished with three or four spines of unequal 

 length, and irregularly disposed towards the extremities. — The 

 smooth nail-like spicule. No. 1, is confined to the body of the 

 sponge, where it forms the chief part of that structure ; while 

 the long arms of the larger ones, which are confined to the 

 surface both on the outside and inside of the cup, have their 

 extremities incurved and buried amongst the surrounding 

 ones. The second, linear or fusiform spicules in their minuter 

 form are confined to the body, where they are arranged vertically, 

 and for the most part parallel to, and in company with, the 

 vertical shafts of the nail-like spicules, appearing, as before 

 stated, in a line round the outer border of the margin of the 

 cup, then disappearing on the convexity of the body, and re- 

 appearing in their largest forms towards its lower third, 

 finally ending in the thick long tuft at tlie base. No. 3, the 

 minute plumose nail- like spicule, is confined to the surface, 

 where the concavity formed by the advanced direction of the 

 arms of the head is applied, through tlie dermal sarcode, to 

 the arms of the large nail-like spicules of the body, or, as 

 before stated, is fixed in the dermal sarcode between the 

 interstices of the latter, where the arms lie parallel to each 

 other for their lohole extent. Of the exact position of No. 4, 

 the birotulate spicule, I am not certain, because the surface 

 ones have for the most part fallen out ; but, judging from its 



