PROP. P. M. DUNCAN ON THE GENUS BIRRHOPALUM. 491 



diameter, but is four or five lines longer (PI. XXIX. fig. 29). 

 The third kind is a very minute fusiform spicule, sharper at one 

 end than at the other. 



Amongst the whorls of spicula are some differing in shape and 

 dimensions from the majority. They are placed between the 

 radiating skeletal elements, and are free in the sarcode which 

 unites the whole. They are much shorter and slenderer than the 

 others, and are cylindrical and very slightly curved at one end. 

 Some of them are about one third the diameter of the whorled 

 spicula, and others are less than one sixth, appearing to be almost 

 linear under a quarter-of-an-inch object-glass (PI. XXIX. figs. 

 22, 23). Larger than these, but still not equalling in breadth 

 the common whorled spicula, are some cylindrical spicules with 

 slightly bent ends, the shaft being very sparingly and minutely 

 spinulate, but not the end (PI. XXIX. fig. 21). Larger cylin- 

 drical spicula are rare ; they are straight, and minutely and 

 sparsely spined, and only on the stem ; their diameter is greater 

 than that of the whorled series, and is about equal to that of the 

 curved cylindrical body-spicula (PI. XXIX. fig. 20). 



The second species was found on the septum of a dead manga- 

 nese-covered coral, dredged up from 1095 fathoms, the locality 

 being off the coast of Spain, No. 17 dredging, 1ST. lat. 39° 30', 

 W. long. 9° 39'. 



The sponge covers a largo septum, is of a dirty-white colour, 

 and is hirsute, with separate long acuates, which arise as it 

 were out of a stubble of smaller spicula, grouped so as to 

 radiate upwards and outwards, from near the base of the long 

 spicula. Each long spiculum has thus a group of shorter ones 

 around it, assuming the direction just mentioned. On separa- 

 ting these structural elements from the coral, a layer of large, 

 curved, or bent, or nearly straight, cylindrical spicula, with one 

 well-developed globose head at least, becomes visible ; they rest 

 on a membranous-looking derm, which is closely applied to the 

 dark-coloured coral-surface. No oscules or pores can be distin- 

 guished, and there is no keratose fibre. 



The curved body-spicula (PI. XXIX. fig. 34) are large, and often 

 T -J-jj inch in length ; they are, in some instances, symmetrically 

 curved, and have a rounded globose termination at either end y 

 which is joined to the body by a very slight constriction. There 

 is a small and close spinulation on the ends, and a larger and 



