62 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



or less transverse; the opesia is trifoliate, the operculum very small (0.08 

 mm wide), semicircular and attached to conspicuous cardelles. Avicu- 

 laria and spines wanting. 



The species is known from the Mediterranean Sea, the Gulf of Mexi- 

 co and Australia. 



Hancock Station 1662-48, Santa Cruz Island, southern California, 

 23 fms, several colonies on shells. Also one colony on a shell from San 

 Felipe, Mexico. 



Genus MEMBRANIPORIDRA Canu and Bassler, 1917 

 "The operculum always closes the ovicell. No dietellae. No avicularia. 

 One large distal septula; two pairs of lateral septulae" (C. and B.). 

 Genotype, M. porrecta Canu and Bassler, 1917. 



The ovicell is hyperstomial but is deeply excavated in the base of the 

 distal zooecium, seeming to extend almost to the dorsal wall. The genus 

 appears much like Alderina, with which it may readily be confused, but 

 there are no dietellae and the ovicell is closed by the operculum. 



Membraniporidra porosa new species 

 Plate 6, fig. 1 



Zoarium forming a thin incrustation on a gastropod shell. 



Zooecia large, 0.75 to 0.90 mm long by 0.55 to 0.65 mm wide ; very 

 distinct, the walls sloping strongly inward and upward, and separated 

 by a broad and deep sulcus ; the mural rim and small gymnocyst smooth 

 and shining ; cryptocyst slightly granulated (scarcely evident) . The mural 

 rim is thin, without spines (one zooecium bears a pair of small tubercles 

 opposite the distal end of the operculum ; these are on the outside of the 

 mural rim and do not rise above its level). The opesia is large, length 

 0.65 to 0.80 mm, width 0.45 to 0.55 mm, rather regularly elliptical in 

 form. The frontal ectocyst is moderately thick and pale yellow in color ; 

 the operculum more heavily chitinized and with a thickened brown 

 border, width 0.20 mm. No avicularia. No dietellae. 



The ovicell is hyperstomial, closed by the operculum, prominent, sub- 

 globular, thick-walled, smooth and shining and perforated by numerous 

 pores ; width 0.30 to 0.35 mm, length 0.25 to 0.30 mm. 



This species is placed in the genus Membraniporidra because of the 

 absence of avicularia and spines and the presence of a hyperstomial ooeci- 

 um closed by the operculum. The general appearance of the zooecia is 

 similar to that of species of Aplousina, but the well-developed hyper- 

 stomial ooecium excludes it from that genus. The perforation of the 



