Zoology.] NATURAL HISTORY OF VICTORIA. [Polyzoa. 



back to back. Tlie specimens are sometimes of considerable size, 

 and one presented to the Museum by Mr. Goldstein forms an 

 irregular foliaceous mass measuring about 13 inches long by 9 

 inches wide and 6 inches liifj;li. 



The cells are large, mostly quadrate, the margins thick and 

 raised, and with the external memljrane tightly stretched across the 

 aperture. The movable lip is very large, occupying about half 

 the aperture, and is of two forms. Most of the cells are quadrate 

 at the anterior extremity, and in these the square operculum is 

 strengthened by a fine band at a little distance from and nearly 

 parallel to the margin. Other cells, usually of a larger size, and 

 frequently situated at the bifurcation of a series, are rounded in 

 front ; in these the operculum is strengthened by two bands, which 

 converge from the base in an arched form, and when close to the 

 margin slightly diverge again, becoming blended with the marginal 

 corneous rim. This form of operculum is generally finely denti- 

 culate at the margin. When the outer membrane is removed, the 

 margins of the cells are seen to be thick, calcareous, the portion 

 behind the attachment of the operculum bevelled inwards, the 

 bevelled surface being finely granular ; the part corresponding to 

 the margin of the operculum forms a smooth, deeply vaulted arch, 

 the posterior angles of which are produced into a tul^ercle on each 

 side for the attachment of the corners of the lip. The inner wall 

 is a thin calcareous lamina, pierced by numerous white-bordered 

 pores ; it recedes downwards and forwards, the anterior part being 

 very abrupt, and opens by a nearly circular sloping mouth, with 

 raised cylindrical margins. Immediately behind this opening a 

 square plate extends upwards and backwards to the articulating 

 base of the operculum, its lateral edges being turned down and 

 united to the lamina so as to form a sort of recess or pouch. The 

 posterior part of the raised inner orifice is united to this plate. 



Explanation of Figures. 



Plate 60. — Figr. 1, specimen, natural size. Fig. la, portion, magnified, showing membranous 

 layer, two sorts of cells, the one quadrate with smooth-edged opereula, strengthened by a 

 square-shaped horny band, parallel to and at a little distance from the margin, the other rounded 

 anteriorly, with rounded denticulate opercula and different sliaped strengtlioning bands. Fig. 

 l/>, portion denuded of membrane, magnified. Fig. \c, two quadrate cells from the same, more 

 highly magnified, showing the raised bevelled edges, the receding perforated calcareous wall, the 

 internal mouth and the plate to the articulating base of the operculum with its edges turned 

 down and continuous with the front of the lamina. 



[ 44] 



