328 PLATE XC. 



the dermal rete ; spicula subfusiformi-acuate ; bases 

 occasionally sub-clavate. Interstitial membranes. — 

 Tension spicula same size and form as those of the 

 skeleton, dispersed, numerous ; retentive spicula same 

 as those of the dermis. 



Colour. — In the dried state, light ochreous yellow. 



Habitat. — Diamond Ground off Hastings ; J. S. 

 Bowerbank. 



Examined. — In the dried state. 



This sponge is parasitical on the branch of a sertu- 

 laria, embracing it closely for about two inches of its 

 height ; the surface is quite smooth, and with the aid 

 of a two-inch lens has much the same finely reticiUated 

 appearance as that of a specimen of Halichondria 

 pamicea, for which, under these circumstances, it might 

 be readily mistaken. The oscula are fcAY and simple 

 in their structure. In a piece of the dermis mounted 

 in Canada balsam many of the triangular areas of the 

 confluent rotulas were furnished with from one to three 

 or four open pores, while in other such spaces none 

 were apparent. The most striking character in this 

 remarkable sponge is in the structure of its dermis, 

 which consists of a thin transparent membrane and a 

 regular and beautiful reticulated structure in the form 

 of a series of hexradiate confluent rotulate areas, the 

 interspaces between the radii being always of a trian- 

 gular form. The effect as presented to the eye by the 

 outer surface of a small piece of the dermis mounted in 

 Canada balsam is very remarkable. Each of the con- 

 fluent areas appears perfect in itself, while at the same 

 time each of it forms, as it were, a part of a neigh- 

 bouring area. The fibre of the rete is multispiculous, 

 compact, and very uniform in its diameter, so that the 

 whole structure presents a very regular and beautiful 

 appearance. 



I liave never met with this structure in the dermis 

 of any other sponge ; but it is a remarkable fact that 

 the wliole of tlic skeleton of the siliceo-fibrous sponge 

 from Porto Rico, in the Museum of the Jardin dcs 



