Australian Poly zoo. . 141 



PETRALIA, New Genus. 



Polyzoary erect, expanded, stony, reticulate, formed of a 

 single layer of cells, placed horizontally side by side, and 

 distinct through the whole thickness of the polyzoary. 



The only other genus of Escharidee, with a reticulate 

 polyzoary, the cells of which are arranged in one plane, is 

 Retepora. The arrangement of the cells is very different in 

 the two genera. In Retepora they are oblique, and rest on 

 a common calcareous base, while in Petralia there is no such 

 basis, but each cell is as distinct on the back of the poly- 

 zoary as in the front. 



P. undata. 



Fenestrse elliptical ; a large avicularium at the base of 

 each in front. Cells quadrate, expanded above, slightly 

 narrowed at the middle and below, separated by narrow 

 raised lines ; front areolated ; mouth circular, with a short, 

 broad, transverse avicularium immediately below the lower 

 lip ; behind, the cells are quadrate, deeply areolated, and 

 separated by deep channels, at the bottom of which is a 

 narrow elevated ridge. Ovicell large, granular ; frequently 

 one or two immovable processes surmounted by sessile 

 avicularia rise from various parts of the ovicell, and 

 there is generally one on each side of the mouth of the cell 

 above which the ovicell is situated. 



Queenscliff ; Portland, Miss F. Birkett. 



Family CRISIIDjE. 

 Genus CEISIA, Lamouroux. 

 G. setosa. 

 Cells 6-10 in an internode, closely adnate, upper extremity 

 usually free for a very small extent ; mouth circular, entire ; 

 cell prolonged outside the mouth, into a stout projection 

 to which is articulated a long hollow calcareous spine. Sur- 

 face finely and minutely granular. Branches usually given 

 off between the first and second pairs of cells in an inter- 

 node. Joints brown. 



A small species, parasitic on algae and zoophytes. 



C. biciliata. 

 Cells two in an internode ; outer extremity free for a 

 short distance ; mouth circular ; from the outside of each cell 

 arise two long, hollow, jointed, filiform processes. Surface 

 granular. Joints of polyzoary and cilia light brown or 

 white. 



