Zoologij.] NATURAL HISTORY OF VICTORIA. \Volyzoa. 



Plate 60, Fig. 2. 

 PETE ALIA UNDATA (P. MacGil.). 



[Genus PETRALIA (P. MacGil.). Sub-kingd. Mollusca. Class Polyzoa. Order Infun- 

 dibulata. Sub-ord. Cheilostomata. Fam. Escharidse.) 



Gen. Char. — Polyzoary stony, expanded, erect, fenestrate, formed of a single layer of cells 

 placed horizontally side by side and distinct throughout the whole thickness of the polyzoary.] 



Description. — Fenestra broadly elliptical, margins tubercular, and with one or 

 two large avicularia at the base of each in front. Cells quadrate, expanded above, 

 slightly narrowed at the middle and below, separated by narrow raised lines ; front 

 tubercular and perforated ; mouth circular, with a short broad transverse avicularium 

 immediately below the lower lip. Behind, the cells are quadrate, deeply areolated 

 and separated by channels, at the bottom of which is a narrow elevated ridge. 

 Ovicells large, globular, closely punctate ; frequently one or more immovable pro- 

 cesses, surmounted by sessile avicularia, rise from various parts of the ovicell. 



Reference.— P. H. MacGillivray, Trans. Roy. Soc. Vict., 1868. 



Portland, Miss F. Birkett ; Queenscliff. 



The polyzoary forms an expanded wavy frond, probably of 

 considerable size, as all the specimens I have seen are broken on 

 the edges. The avicularia occur in three different forms. Imme- 

 diately below the mouth of each cell is a short transverse sessile 

 avicularium, and at the lower edge of each foramen one or two 

 large sessile avicularia take the place of ordinary cells. In addition 

 to these the ovicells have usually one or more calcareous processes 

 on various parts of the surface, each surmounted by a small sessile 

 avicularium. The ovicells are crowded in patches, frequently united 

 to each other, and on the cells supporting them are numerous 

 sessile avicularia, usually on raised calcareous bases and generally 

 arranged along the margins and round the mouths. 



The only other genus of Escharidce with a foraminate polyzoarv, 

 the cells of which are disposed in one plane, is Retepora. The 

 arrangement of the cells, however, is very different in the two 

 genera. In Retepora they are oblique and rest on a common cal- 

 careous basis, while in Petralia there is no such basis, but the cells 

 are horizontal and as distinct on the back of the polyzoary as in 

 the front. 



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