MEMBRANIPORA. 127 



The avicularia in this family almost always exhibit a 

 more highly specialized form than in the preceding. They 

 are usually secondary formations^ borne upon the zocecia 

 instead of being developed in the same plane with them. 



In a great proportion of cases the colonies in the 

 present family^ and indeed very commonly amongst the 

 Cheilostomata at large, originate in a peculiarly shaped 

 cell, which differs widely from the mature zocecium. 

 And these primary cells exhibit^ with minor differences, 

 a general similarity of structure. They are for the most 

 part somewhat rounded, Avith a large terminal aperture, 

 closed in by a membrane, and usually surrounded by a 

 number of spines. Such a form was long since described 

 by Van Beneden as a distinct genus, under the name of 

 Tata^; and the original cell of the Cheilostomatous colony 

 is often distinguished as the Tata-iorm. Of course this 

 genus, being founded on an early and immature condition, 

 which is common to a large section of the Polyzoa, has 

 not been maintained. I have designated the first element 

 of the Cheilostomatous colony the primary cell ; and if a 

 separate name is needed for the form which it generally 

 assumes, it may be styled the Tata-stage. 



Genus MEMBRANIPORA, Blainville. 



Der. From ?nembrana, a thin skin, and poms, an opening. 



EscHARA (part.), Pallas. 



Flustra (jjart.), Linn. : Lamarck: Fleming: Lamouroux : Audoiiin. 

 Membranipoea, Blainville, Man. d'Actinol. : Johnston : Busk : Smitt : &c. 

 DiscoPORA (part.), Lamk. An. s. V. 



* " Eeeherches sur les Pol. Brjozoaires de la mer du Nord," Bull. Ac. 

 Roy. Belg. xvi. no. 12 (1849), p. 6 (sep.). 



