130 MEMBHANIPORID^. 



Membranipoea Peacuii, Couch, Corn. Faun. iii. 120, )d1. xxii. fig. 13. 

 ?Membranipora membranacea, Johnst. B. Z. 2 ed. pi. Ivi. figs. 11, 12. 

 CoNOPEUM reticulum. Gray, B.M. Kad. 108. 

 Membranipora Lacroixh, Busk, B.M. Cat. ii. HO, pi. Ixix., pi. civ. fig. 1 : 



Hincks, Dev. Cat., An. N. H. ser. 3, ix. 28 (38 sep.). 

 Membranipora reticulum, Eetiss, Foss. Polyp, d. Wiener Tertiarbeck. 98, 



pi. xi. fig. 25. 

 BiFLUSTRA Lacroixh, Smitt, Flor. Bryoz. pt. ii. 18, pi. iv. figs. 85-88. 



Zooecia oval, sometimes much elongated, area occupying 

 (usually) tlie whole of the front of the cell, with a 

 membranous covering ; or occasionally a calcareous 

 expansion round the inner edge ; margin slightly 

 thickened, rounded, granulated, rising, so as sometimes 

 to form a prominent ridge ; often armed with two erect 

 spines, one on each side above, more rarely bearing a 

 considerable number (about eleven), very delicate and 

 sharply pointed ; frequently a triangular hollow on each 

 side, immediately above the aperture. Ocecia none. 



Colonies forming a thin gauze-like crust over shells 

 and stones, often of great extent. 



Range of Variation. The front of the cell is either a 

 very regular oval or much elongated and narrowed. It 

 is generally occupied entirely by the aperture ; but occa- 

 sionally the zooecium is slightly produced below. The 

 cells lie very closely together in most cases ; and speci- 

 mens are rarely met with in which they are mo)'e or less 

 disjunct. The spines vary in number from two to about 

 a dozen. Usually they are represented by the couple at 

 the top of the cell ; but in sheltered situations the mar- 

 gin bristles with slender spinules, and in most colonies 

 cells may be met with on which a few at least survive. 

 The hollow triangular spaces above the aperture are ofteu 

 wanting. They are not true avicularia, but consist of a 

 three-cornered area inclosed by calcareous walls, and 

 covered in by a transparent membrane. This membrane 

 is frequently destroyed; and they then appear as holloAV 



