Zoology.'] NATUKAL HISTORY OF VICTORIA. IPohjzoa. 



Plate 57, Fig. 1. 

 BIFLUSTRA PERFRAGILIS (P. MacGil.). 



[Genus BIFLUSTRA (D'Orbignt). (Sub-kingd. Mollusca. Class Polyzoa. Order Infun- 

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



Gen. Char. — Polyzoary usually consisting of two layers of horizontal cells placed back to 

 back and easily separable, occasionally of a single adnate layer ; cells large, more or less 

 quadrate, with rigid raised margins, and the front partly occupied by a broad, usually granular 

 lamina.] 



Description. — Cells much elongated, slightly arched above, raised margins 

 minutely granular ; the lamina smooth or finely granular, occupying about the lower 

 third of the front of the cell, and extending as a narrow rim a short distance up the 

 sides, leaving an oval or elliptical aperture. 



Eeference. — B.fragilis, P. H. MacGillivray, Trans. Roy. Soc. Vict., 1868. 



King's Island, Bass's Straits ; Port Phillip Heads. 



This species is usually found in two layers of cells, the resulting 

 lamina being variously twisted and united so as to form an ex- 

 tremely delicate cavernous polyzoary. This double arrangement is, 

 however, not constant, and I have a specuuen of Eschara mucronata 

 on the surface of which a single layer has extended from a mass of 

 the ordinary double form. The cells are elongated, usually about 

 three times as long as broad ; the raised margins and lamina are 

 nearly smooth or very finely granular. In some specimens, how- 

 ever, the cells are shorter, the ridges and lamina stronger, and the 

 granulations coarser, approximating to the structure in the next 

 species. 



Explanation op Figures. 



Plate 57. — Fig. 1, specimen, natural size. Fig. la, portion, magnified. Fig. \b, single 

 cell from same specimen, more highly magnified. Fig. Ic, two cells from another specimen, 

 with the membrane filUng the aperture entire, and showing the mouth at the upper part. Fig. 

 \d, section, showing the sides of the cells. Fig. le, section, showing the ends of the cells. 



* In different descriptions "zoarium" Is used for "polyzoary," "zooecium" is used for "cell," and " ooeciuin " Is used 



instead of " ovicell." 



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