28 THE CRAG POLYZOA. 



Genus 1. Membranipora. 



Polyzoario diffuso ; cellulis antice depressis, ssepius plus, minusve membranaceis 

 sive apertis, margine elevato circumdatis. 



Polyzoarium encrusting, spreading irregularly. Cells more or less irregularly disposed 

 or quincuncial ; margins raised ; front depressed, often more or less membranaceous or 

 open in front, 



EscHAKA (pars), Pallas. 



Flustra (pars), Linn.; Muller ; Esper ; Lamarck; Grant; Fleming; Risso ; Johnst., 



Transact. Newc. Soc. ; Lamouroux, Hist. d. Polypes, p. 96. 

 Membranipora, Blainville, Man. d'Actinol., p. 447; Johnston; Busk, B. M. Cat., p. ii, 



p. 56; W. Thompson ; Hassall ; Reuss (1851, not 1847). 

 Cellepora (pars), Hag enow ; Reuss; D'Orbigny. 

 DiscopORA (pars), Lamarck, An. S. V., ii, p. 248, 1836. 

 Annulipora (sp.). Gray, Append. B. M. List. 

 CoNOPEUM (sp.). Gray, ib. 

 Callopora (sp.), Gray, ib. 

 Amphiblestrum (sp.), Gray, ib. 

 MiCROPORA (sp.), Gray, ib. 

 Margin aria (pars), Rcemer ; Hagenow. 

 Dermatopora (pars), Hagenow. 



In the genus Membranipora, the polyzoarium is adnate, creeping in an irregular 

 manner over the surface of rocks, shells, or fuci. The cells are contiguous, sometimes 

 disposed in parallel lines or series, sometimes very regularly quincuncial. The peculiar 

 characters of the cell itself consist in its being either much depressed or partially open 

 in front, that is to say, the calcareous wall of the cell is deficient for a greater or less 

 extent, the vacancy or " aperture " being occupied in the recent state by a thin chitinous 

 membrane, in which is placed the true orifice, with its moveable lip. In many cases, 

 however, in advanced age the membrane becomes more or less completely calcified, but 

 in this case the character of the genus is still manifested in the persistent elevated border 

 which surrounds the cell, and constitutes a sort of frame. Some of the species are 

 variously armed with spines, tubercles, and avicularia, whence good specific characters are 

 derivable. Some exhibit very great varieties of aspect, according to their age, the 

 situation in which they have lived, or the greater or less degree to which they may have 

 been exposed to various external influences ; and so great is this variety that it is diflicult, 

 even in recent or living forms, always to be certain of any given specimen. Numerous 

 species, both recent or fossil, have been described, and their appearance on the globe appears 

 to date from the Cretacean period. But among the fossil forms, belonging more especially 



