ART. 13 BRYOZOAN FAUNA CANU AND BASSLER 7 



the great southern current has modified considerably the nature of 

 the plancton and all the marine fauna. The simple forms indifferent 

 to the thermic influences alone have been able to persist. This is 

 precisely the case for Aplousina -filum. 



Occurrence. — Galapagos Islands, D. 2813, 



Geographic distribution. — Eastern Atlantic: Cape Verde Islands, 

 80-180 meters; Azore Islands, 130-318 meters; Cape Spartel, north- 

 west of Morocco, 717 meters. Mediterranean: Corse, littoral; 

 Capri (?). Western Atlantic: Florida, 13-60 fathoms. Pacific: 

 Galapagos Islands, 40 fathoms. 



Plesioty pes. —C2it. No. 8470, U.S.N.M. 



Genus MEMBRENDO'ECIUM Canu and Bassler, 1917 



MEMBRENDOECIUM CLAUSTRACRASSUM, new species 



Plate 1, Figures 3-7 



Description. — The zoarium is multilamellar; it incrusts fragments 

 of shells and dead gastropods. The zooecia are oval, the point above, 

 a little enlarged at the base, elongated, distinct, separated by a deep 

 furrow. The mural rim is a thin salient thread; the cryptocyst 

 almost entirely surrounds the opesium; it is very much enlarged 

 proximally and is finely granular. The opesium is elongated, oval, 

 distally adjacent to the mural rim, finely crenulated. At the base 

 of each zooecium there is a small triangular avicularium oriented 

 longitudinally, the beak above. The opercular valve is small, re- 

 moved from the mural rim laterally. The ovicell is endozooecial, 

 little apparent, covered by a small chitinous band distally and a 

 large, thick, and much chitinized opercular valve. 



Measuremen ts. — 



^ . [7io = 0.26-0.30 mm. ^ . fZs = 0.40-0.50 mm. 

 ^P^^^^^^l 7. = 0.16-0.18 mm. ^"^^^^^ { Z.==0.30mm. 



Structure. — The structure of the ovicell is quite remarkable and 

 can be seen only on the specimens preserving their ectocyst. It is a 

 simple distal cavity covered by a chitinous band and by a large 

 hinged operculum thicker and more chitinized than the small oper- 

 cular valve of the other cells. It is therefore little visible on speci- 

 mens deprived of the ectocyst, although the doubling of the small 

 distal avicularium is often an index of its presence. 



Certain zooecia have their cryptocyst perforated by a small sub- 

 circular median opesium; they are not regenerated and we are still 

 ignorant of their anatomical structure. The ancestrula is very small ; 

 unfortunately our specimen does not show this structure very well. 



