a General History of the Marine Polyzoa. 149 



the neighbouring interspace, and lies quite on a level with the 

 rim of the margins. 



Memhranipora bellula, n. sp. 

 (PI. VIII. figs. 4, 4a, 4b.) 



Zooecia pyriform, rounded and expanded above, and narrow- 

 ing off to the base ; area occupying about half the length of 

 the cell, wholly filled in with membrane, subelliptical, broad 

 below and narrowing very slightly upwards to the top, where 

 the semicircular orifice is placed, flanked on each side by two 

 tall erect spines ; on the lower margin a single, much -branched 

 spine, which spreads over the aperture, forming an antler-like 

 operculum ; sometimes a very long corneous spine, springing 

 from a raised socket, a little below the inferior margin ; 

 portion of the cell below the area, which is sometimes a good 

 deal elongated, smooth and shining, and covered with nume- 

 rous delicate spinules. Ooecta none. 



Var. a {hicornis). With two opercular spines on the lower 

 margin, of small size and slightly branched, placed one on 

 each side of a short, sharply pointed central mucro rising from 

 a prominent boss ; a single spine only on each side of the 

 orifice; no spinules or horny appendages; surface smooth, 

 white, and very polished. 



Var. /3 [multicornis) . Opercular spines 3-5, placed closely 

 together, their numerous dichotomous branchlets combining 

 to form a beautiful protective shield, which extends to the 

 base of the oral valve. 



Loc. Australia, normal and var. muMcornis ; Ceylon, var. 

 hicornis ; Madagascar [Miss Jelly) ; St. Vincent, Cape- Verd 

 Islands {Miss Gatty). M. hellula always occurs creeping 

 over weed, and frequently runs out into narrow strap-like 

 segments. 



This is an exquisite species, which seems to be far from 

 uncommon in various parts of the world ; and it is difficult to 

 understand how it is that it has remained so long undescribed. 

 I cannot recollect, however, to have met with any published 

 account of it, although it has been known to collectors under 

 a manuscript name. It is a species which varies much in 

 appearance, the changes being chiefly due to the presence or 

 absence of the spinous appendages, and especially to the modi- 

 fication of the opercular spine. The principal varieties have 

 already been noticed. In some cases the tall corneous spine 

 rising from a distinct socket, which is so characteristic of M. 

 pilosa (from which the present form is probably derived), 

 makes its appearance ; in others the zoarium bristles with 

 immense numbers of slender spinules ; in others, again, it has 



