1^08] Bohertson. — Incrusting Bryozoa. 257 



Membranipora Blainville. 



Eschara (part) Pallas, 176G. 

 Membranipora Blainville, 1834. 

 Membranipora, Johnston, 1847. 

 Cellepora d 'Orbigny, 1850-52. 

 Membranipora, Busk, 1854. 

 Membranipora, Sniitt, 1867. 

 Membranipora, Hincks, 1880. 



Zoarium incrusting, sometimes adhering closely to the substra- 

 tum, sometimes almost free. Zocecia alternate, arranged in linear 

 series and often radiating from a central, primary zooecium; 

 margins raised and more or less calcareous. Aperture membran- 

 ous, depressed, usually occupying the whole of the front of the 

 zo(jecium ; if occupying but part, the remaining portion covered 

 by a delicate calcareous lamina. 



The Memhraniporce of the Pacific coast are for the most part 

 incrusting, one species only M. serrata Hincks, sometimes forming 

 two-layered foliaceous expansions. An approach to this latter 

 condition is seen in one other species, 31. sandalia Robertson 

 ('00), which forms a loosely adherent crust. The colonies of 

 this genus, and of many other incrusting genera, originate in a 

 zooecium of simple form known as the primary cell or zooecium, 

 and spoken of by some writers as the Tata cell. This is usually 

 entirely memlu-anous and possesses many spines on its margin, 

 often differing widely from the adult zooecium. PI. 18, fig. 36 

 represents the Tata stage of Microporella malusi, a species some- 

 what distantly related to Mcmhranipora. 



The Chilostomaia and the bryozoa in general, possess a lar- 

 val stage of greater or less length. The egg develops, sometimes 

 in a special receptacle, the oo-cium, sometimes in the zooecium it- 

 self, or perhaps in the water, into a ciliated, swimming larva. 

 IMost of these have short existence as free swimming organisms. 

 Many, after a free life of only a few hours or minutes even, settle 

 upon a suitable surface and are quickly transformed into the first 

 or primary zooecium, the starting point of a colony. The Mem- 

 braniporm are interesting as being the only genus among the 

 Chilostomaia which possesses the remarkable larva known as 

 Cyphomintcs. This organism is inclosed in a bivalve shell, pos- 



