NO. 1 OSBURN : EASTERN PACIFIC BRYOZOA CHEILOSTOMATA 19 



Knobs or tubular spines, if present, developed usually by the 



folding of the distal rim, gymnocyst usually wanting 



Membranipora 



Genus MEMBRANIPORA Blainville, 1830 



Biflustra A' Oxhigny, 1852. 



Nitscheina Canu, 1900 (Nichtina by error, according to Canu). 



Acanthodesia Canu and Bassler, 1920. 



Blainville erected the genus Membranipora to include 6 species all of 

 which, except membranacea Linnaeus, have been placed elsewhere, leav- 

 ing membranacea as the genotype. 



Canu, under the impression that Membranipora was not properly 

 founded, replaced it by Nitscheina {Nichtina by a printer's error) with 

 M. membranacea as the genotype. 



Biflustra d'Orbigny was not figured ; the description is unrecogniz- 

 able, was apparently meant to include bilaminar forms, and has been 

 discarded. 



Canu and Bassler separated Acanthodesia from Membranipora or 

 Nitscheina {Nichtina) by the following diagnosis: "No ovicell. The 

 opesium is garnished laterally by small spinous processes and inferiorly 

 by a serrate denticle. Fifteen tentacles." The description was based on 

 Flustra savartii Audouin as the genotype and no other species included. 

 Since 1920 Canu and Bassler, Harmer, Hastings, Marcus and Osburn 

 have added numerous species with the lateral cryptocystal spinules. 



Borg (1931:1-30) has thoroughly investigated the status of Flustra 

 membranacea Linnaeus and the species with which it was confused by 

 older authors and concludes that Membranipora is a good genus with 

 membranacea, as now understood, as the genotype, an opinion with which 

 the present writer is in accord. 



With Biflustra and Nitscheina discarded, the only question that re- 

 mains is that of the status of Acanthodesia and, frankly, I am unable to 

 draw any definite line between Membranipora and Acanthodesia, though 

 if there were not a continuous series of intergradations between membra- 

 nacea and savarti the distinction would be clear enough. 



1. Both species have twinned ancestrulae. 



2. Mural spines are wanting in both. 



3. The gymnocyst is wanting or vestigial. 



4. The cryptocyst is well developed in savarti and barely visible in 

 membranacea, but other species show all the intermediate conditions 

 and the proximal dentate tooth of savarti is frequently wanting on both 



