1898.] NATURAL SCIENCES OP PHILADELPHIA. 431 



a hard stony mass by a secondary deposit of silica which encrusts 

 and cements them, with the formation of numerous synaptacula 

 (Plate XX, fig. 6). Regular or modified hexacts are occasionally 

 found wedged in interstices, but the appearance is that the demalia 

 and hypodermalia have been worn or decayed away from this region. 



The sponge body or stalk rises from near the centre of the base 

 to a height of 16 inches. Its summit is frayed out and must have 

 been originally at least an inch higher. It is terete and tapers gently 

 and regularly from the base, which is H of an inch in diameter, to 

 the broken apex, f of an inch in diameter. A well developed 

 gastral cavity extends through the sponge body from base to sum- 

 mit, so that it is hollow throughout. Toward the base the walls 

 are thick and firm, owing to secondary incrustations of silica, while 

 above they are much thinner and quite friable. 



The lower 3} inches of the body have a texture and appearance 

 similar to the base, but the transition to the branched upper region 

 is gradual. A very few short blunt spines are borne on the sponge 

 wall, and these partake of the stony hardness and silicious incrus- 

 tations which characterize the walls of this region. Two longer 

 spines, having more of the character of the upper branches, are 

 present, the first 1 inch, and the second 1\ inches above the base. 

 These are respectively I and 4 of an inch long. The former is 

 situated just above the first crater-like opening in the sponge walls. 

 This region of the sponge has a smooth hard surface, and like the 

 basal portion lacks the superficial layers of spicules. 



At about 3£ inches above the base, loose flesh spicules become 

 more plentiful and soon form a thick soft layer, looking very much 

 like a covering of a fine cotton wool paste, or as if the specimen had 

 been dipped into a thick soap lather, which had been allowed to dry 

 on its surface. Coincident with this change in the character of the 

 surface, spinous processes become more numerous and very much 

 longer, but in this specimen the lower spines are imperfect. While 

 in the lower portion (i) of the sponge the processes remain compar- 

 atively simple and unbranched, those which densely cover the upper 

 half of the stalk are often very long (the longest nearly 5 inches 

 and r6 of an inch in diameter at the base), much and complexly 

 branched, sometimes to the third order. Wherever such branches 

 cross they are united by secondary anastomoses, due to the concre- 

 sence of the parenchyma. The principal branches vary in diameter 

 from iV to h of an inch, but two may fuse at their bases and form 



