144 Dr. W. C. M'lntosh on the Invertebrate 



Hymeniacidon celata, Grant ; Bowerb. vol. ii. p. 212. 



Abundant in shells from deep water, between the layers of 

 which it tunnels its devious tracks. This is one of the main 

 agents in causing the disintegration of dead shells. 



Halichondria 'panicea^ Pallas ; Bowerb. vol. ii. p. 229. 



Scarcely a stone can be lifted near low-water mark, amongst 

 the rocks, but has a patch of this common sponge. Under 

 the cavernous ledges overhanging rock-pools it spreads its 

 structure over the dark red Cynthia, matting together sea- 

 weeds and corallines, and hanging in pendulous nodules on 

 interwoven stalks of Corallina officinalis and Fuci. Near the 

 Maiden Rock splendid specimens are found incrusting a square 

 foot or two of rock in some of the quiet pools. It also abounds 

 on the backs of crabs, such as Hyas araneus and Inaclms 

 dorynchus, covering the former so completely that it can 

 scarcely be recognized except by its legs ; and besides the pro- 

 minent oscula of the sponge, on this complex back are gaps 

 for Balani, shells, and seaweeds. On the carapace of the latter 

 species it forms a thinner coating, but is likewise grouped in 

 little nodules on the legs, A mass as large as a good-sized 

 apple surrounds the stem of Chalina oculata ; and it is a com- 

 mon envelopment of various stones, moUusks, seaweeds, and 

 tangle-roots. The usual colours of the sponge are yellow, 

 brown, purple, green, and grey. In the interstices of the 

 masses thrown on shore at the West Sands are to be found mul- 

 titudes of marine animals, besides incorporated shells ; and the 

 fine patches at the East Rocks are favourite feeding-grounds of 

 Doris tuherculata. The forms of the spicula of this species 

 are variable, some being much curved like a stretched bow, a 

 few more or less insequiacerate vermiculoid, besides, of course, 

 the ordinary diagnostic spicula. The odour emitted on tearing 

 it from the rock is characteristic, but causes no sneezing. 



Halichondria J n. s.* 



The following is Dr. Bowerbank's description : — " Sponge 

 coating, thin. Surface smooth and even. Oscula more or 

 less elevated, dispersed, margins thin. Pores inconspicuous. 

 Dermal membrane aspiculous. Skeleton very irregular, rete 

 mostly unispiculous, occasionally bi- or trispiculous ; spicula 

 acerate, short and stout. Interstitial membranes aspiculous. 



" Colour in the dried state light nut-brown. Examined in 

 the living and dried states. 



" The nearest alliance with the known species of the first 



* Dr. Bowerbank has courteously named this species H. M'Intoshii, 

 Bowerb. 



