69 



coarsely fibrous and coralloid in appearance, having numerous grains 

 of sand separately imbedded in its substance, the whole being enve- 

 loped by the homy matter of the fibre. Spicula rare, short, slightly 

 curved, terminating somewhat obtusely. 



The base of this specimen has been destroyed by the action it has 

 apparently undergone among the shingle ; but its position is well 

 marked by the concentration of its fibres at the point at which, from 

 its form and other circumstances, we might expect it to have been 

 placed, and there is no indication whatever of its ever having been 

 pedunculated. The form is somewhat fan-shaped or compressed, one 

 side being regular and nearly flat, while the other has a protuberant 

 mass upon its surface. The fibres of the skeleton are coarse and ri- 

 gid, assuming the direction of aberrant lines, radiating from the base 

 of the animal, and anastomosing with each other in every direction by 

 means of small lateral branches ; thus forming a coarse and rigid but 

 somewhat regular reticulated skeleton. The large fibres frequently 

 attain the size of half a line in diameter. If we place a few of these 

 fibres in Canada balsam between two slips of glass, and examine them 

 by transmitted light with a lens of about half an inch focus, we shall 

 readily perceive numerous grains of sand imbedded in the substance ; 

 and if the examination be continued with a microscopical power of 

 about 200 linear, it will be seen that the grains are not imbedded in 

 the fibre from pressure through the external surface, but that they oc- 

 cupy its very centre, and are externally enveloped by a thick coating 

 of the cartilaginous substance of the animal, (fig. 10). In this condi- 

 tion they do not occupy the interior of a central cavity, but are regu- 

 larly built together, with a slight space intervening between each 

 grain, which is filled with dense cartilaginous matter, thus firmly ce- 

 menting the whole into a compact body, while at the same time each 

 grain of sand may be said to occupy its own cell. The mode in which 

 this curious building process appears to be achieved is this. After 

 the cartilaginous matter has entirely enveloped the grain of sand at 

 the extremity of a projecting fibre, there is an accumulation of its 



genus : — Spongia multiformis sessilis crasse cellulosa mucagine sabulo arenata sea- 

 tens, sice friabilis, fibris imperfectis seposita : spiculis sparsis paucis forma et magni- 

 tudine incertis. 



In the Synopsis Spongiarum et Lithophytorum, at the end of the • History of 

 British Sponges and Lithophytes,' the author has altered the name from Duseideia to 

 Dysidea. 



