354 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



the aperture and avicularium without obscuring them (rarely only a 

 median umbo is present). The suboral avicularium is small with a 

 triangular or semicircular mandible directed upward. 



The ovicell, 0.20 mm wide, is hyperstomial, not closed by the oper- 

 culum, covered by a thick layer from the distal zooecium which often 

 leaves exposed a small area of the endozooecium. 



I believe there can be no error in transferring this species to the 

 genus Aimulosia. If the circumoral wall is merely an extension of the 

 sides of the suboral umbo, all of the difficulties in interpretation disappear. 



Hitherto known only from the original record by Canu and Bassler, 

 from the Straits of Florida. 



Hancock Station 143-34. off Wenman Island, Galapagos, 1°23'10''N, 

 91°48'45''W, at 100 fms, several colonies (compared with specimens 

 from Florida Straits) ; and 270, east coast of Angel de la Guardia 

 Island, Gulf of California, 29°3r00"N, 113°27'00nV, at 10 fms. 

 It is probable that the species extends all along the coast from the 

 Gulf of California to the Galapagos Islands, since the colonies are 

 very inconspicuous. 



Genus HIPPOPORIDRA Canu and Bassler, 1927 



Hippotrerna Canu and Bassler, 1927:9, 



"The ovicell is hyperstomial and bears a frontal area. The zooecia 

 are accumulated ; the frontal is surrounded by areolar pores and often 

 bears small avicularia. The aperture is formed of an anter and a 

 poster separated by two cardelles. The large interzooecial avicularia 

 are acuminated," Canu and Bassler, 1927:8. Genotype, Cellepora edax 

 Busk, 1859. 



The frontal is a thick costulate pleurocyst with one or more rows 

 of areolar pores. In the genotype, H. edax, there is usually a single row, 

 but in H. calcarea, H. janthina and H. spiculifera there are some 

 additional pores. The appearance of the last two species misled Canu 

 and Bassler into erecting another genus, Hippotrerna, on the supposition 

 that the frontal is a tremocyst. The study of younger zooecia, however, 

 reveals the fact that in all of the above species the formation of the 

 frontal is identical, the pleurocyst arising from the margin and de- 

 veloping centrally; when additional pores are present the openings of 

 these are carried upward on the front and give the appearance of a 

 tremocyst. In all other characters Hippotrerna is similar to Hippoporidra 

 and should be suppressed. 



