On Baciijlocahjx immiceus {Stutclibunj). By W. J. Sollas. 133 



acerates become involved iu siliceous deposit, and form an integral 

 part of the spine. 



Similar spines were detected on the upper surface of the type 

 specimen of D. pumiceus, but they are much less abundant in it 

 than in its variety D. Stutchhuryi. 



Fig. 3. Fig. 4. 



Fig. 3, Lateral spiue. Fig. 4, Terminal point of a "lantern" spine x 115. 

 The dotted lines indicate the ends, which have been broken off. 



At the bottom of the vasiform cup of D. Stutchhuryi, at one 

 side, is a cylindrical tube ^ an inch in diameter, obliquely perfora- 

 ting the wall from side to side, and in this, as in a similar tube iu 

 D. immiceus, remains of the dermal spicular layer were discovered. 

 A fine collection of the spicules was cut out, but, being blown away 

 by a current of air, was lost, and no subsequent searching succeeded 

 in recovering it. Enough was obtained from what remained, how- 

 ever, to show that the characters of its spicules were the same as 

 those of the dermal layer already described, the projecting acerates 

 and dermal sexradiates both being present ; a larger number of 

 dermal spicules, however, were found with distal and proximal rays 

 aborted, the four rays remaining being spread out horizontally in 

 the dermal surface. 



By holding the sponge upside down, and smartly tapping the 

 bottom of the pedicel, a large number of long acerates were shaken 

 out; they were generally incomplete at one end, and in a single 

 instance one was observed with the extremity rounded off, thus pre- 

 senting us with an acuate variety of this kind of spicule. 



The relations of the excurrent and incurrent canals could be 

 prettily illustrated by holding the sponge up to the light ; looking 

 then into the shaded interior of the cup, one saw ilkimiuated patches 

 opposite the incurrent openings, and these patches always fell on 

 the continuous netwoi'k of the sponge, never coinciding with an 

 excurrent aperture ; when the position of the sponge was reversed, 

 the excurrent apertures similarly cast illuminated images on the 

 surface of the outer ridges, but never coincided with incurrent 

 openings, thus demonstrating the absence of completely perforating 

 canals. Of course the perforating tube previously mentioned is an 

 exception, but then that does not belong to the water-system of the 

 sponge. 



