NO. 1 OSBURN: eastern pacific BRYOZOA — CHEILOSTOMATA 53 



chamber can be seen to develop separately before the zooecium distal to 

 it is calcified. They are therefore definitely interzooecial in origin, what- 

 ever their later surface relations may appear to be. They are not always 

 paired, especially near the center of the zoarium, nor are they always 

 directed toward each other. 



The ooecia are vestigial, represented by a small transverse rib between 

 the avicularia. Dietellae are present. 



Probably distributed around the world in warmer waters ; Madeira 

 and Cape Verde Islands ; Indian Ocean ; Ceylon ; Japan ; East Indies at 

 various localities; and recorded by Hastings from Jicaron Island, Pana- 

 ma. It has not been noted on the Atlantic coast of the Americas. 



Hancock Station 264, south of White Friars Islands, oii Petatlan 

 Bay, Mexico, 25 fms, on a shell, and 457-35, Secas Islands, Panama, 12 

 fms, on shells ; also. Gulf of Panama, Galtsoff collection, on pearl oysters. 



Antropora claustracrassa (Canu and Bassler), 1930 

 Plate 4, fig. 6 



Membrendoecium claustracrassum Canu and Bassler, 1930:7. 



The zoarium encrusts shells, corals and coralline nodules, multi- 

 laminar, white and glistening. The zooecia are of moderate size, about 

 0.40 to 0.50 mm long, but there is much variation; distinct with deep 

 furrows ; mural rim thin ; cryptocyst granular, broad proximally and ex- 

 tending on the sides along the operculum, crenulated on the inner margin. 

 Opesia oval, the distal end narrower. At the proximal end there is, on 

 one or both sides, a small interzooecial avicularium with a triangular 

 mandible which is usually directed straight forward. From their position 

 the avicularia often appear to be frontal, especially when only one is 

 present, but disssection shows the minute cavity of the chamber extending 

 to the level of the dorsal side. 



The ovicell is small, endozooecial and scarcely noticeable, but the 

 operculum of the fertile zooecium is considerably larger and more heavily 

 chitinized. Small dietellae are present. There are no spines, but occasion- 

 ally small nodules occur in place of avicularia. The ancestrula is only 

 about half as large as the later zooecia, but the "false ancestrulae" of the 

 secondary lamina are noticeably larger than the ordinary zooecia. 



Canu and Bassler described the species from the Galapagos Islands. 

 The present work shows it to be a common species, ranging from Guay- 

 mas, Mexico, 27°56'N Lat. to La Libertad, Ecuador and the Galapagos 

 Islands. 



