w ^ n ^ tm mm ^ m 





1 



i 



' 





\ 



THE SPONGES. 



131 



upper is smooth. 



Oscula small and scattered over upper and outer surfaces. Pores 



abundant in meshes of dermal reticulum of upper surface; scattered over lower surface, in 

 places abundant. 



Spicules : Oxea, 320 /x x 20 p, with smaller sizes. Sigmata 18 /x long, abundant. Main 

 skeleton a confused irregular reticulum of spiculo-fibres, with abundant free spicules 

 scattered between the fibres. Fibres consist chiefly of spicules, with only a very small 

 amount of spongin, and in general are not sharply separated from the scattered spicules. 

 On the upper surface is a dermal reticulum of spiculo-fibres from which single spicules 

 and tufts of spicules everywhere project. On the lower surface a dermal reticulum is 

 developed in places, the membrane elsewhere containing only scattered spicules. 



Station given as Panama, 4 specimens. 



The largest specimen, Fig. 1, Plate 18, is an irregular plate, the 

 under surface of which has apparently been moulded over several rounded 

 objects. The plate is 5 to 10 mm. thick, with a greatest width of 95 mm. 

 Perforating spaces 4 or 5 mm. in diameter pass through the body, from 

 the upper to the lower surface. The upper surface, which is the one 

 figured, is very uneven, and from it project numerous lobes having the 

 shape of low rounded or irregular elevations, often with a subterminal 

 osculum. It is apparently the case that such elevations are primarily 

 simple and independent, but in some instances in the course of lateral 

 expansion they meet and fuse with one another, thus roofing in tunnel- 

 like spaces which come to lie between the body of the plate and the fused 

 lobes. On the under surface, too, especially near the periphery, some 

 similar tunnel-like spaces have been formed, apparently by the fusion 

 of lobes growing out from this surface. 



Of the other specimens, two are fragments of similar plate-like masses, 

 and may indeed have been broken off from the larger piece just described. 

 In one of them the perforating spaces, passing through the body from 

 upper to lower surface, are large, reaching 15 mm. in diameter. And 

 the lobes projecting from the under surface, and fusing in the manner 

 described, give the mass a thickness of 30 mm. 



The remaining specimen has a different shape. It is an amorphous 

 mass about 40 mm. in diameter, and consists of a few irregular but in 

 the main subcylindrical lobes, 5 to 15 mm. thick, anastomosing in several 

 planes and thus enclosing spaces which continue to pass quite through 

 the body of the sponge, and have a diameter themselves of 5 to 15 mm. 

 The upper and lower surfaces of the whole mass are readily distinguish- 

 able, resembling the corresponding 



surfaces of the flattened plate-like 



specimens 





