478 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



Family Grepidacanthidae Levinsen, 1909 



The ooecium is hyperstomial and recumbent. Pore chambers and sep- 

 tulae sometimes alternate. Zooecial aperture with strong cardelles ; oper- 

 culum well chitinized. Avicularia long, setose or pediform, usually paired 

 at the sides of the aperture ; long oral spines usually present and some- 

 times marginal spines also. 



Genus GREPIDAGANTHA Levinsen, 1909 



The frontal is surrounded by a row of long setose marginal spines 

 situated between the areolae. Aperture with a very broad poster and 

 without a sinus. Ovicell recumbent, closed by the operculum. Genotype, 

 C. poissoni crinispina Levinsen, 1909:266. 



Grepidacantha poissoni (Audouin), 1826 



Plate 58, fig. 2 



F lustra poissoni Audouin, 1826 : 10. 

 Lepralia poissoni. Waters, 1899 :16. 

 Grepidacantha poissoni, Canu and Bassler, 1929:33. 



Zoarium encrusting, forming small white colonies, usually on shells. 

 Zooecia moderate in size, averaging about 0.55 mm long by 0.40 mm 

 wide, but subject to much variation ; the frontal is smooth, inflated, the 

 separating grooves deep ; a row of small areolar pores. The primary 

 aperture is rounded beyond the strong triangular cardelles, and prox- 

 imally to these is a wide, shallow poster with a straight proximal border ; 

 0.10 mm long by 0.08 mm wide. The peristome is little developed and 

 is unarmed, but a slight umbo usually projects forward just enough to 

 give the proximal border an incurved outline. A pair of setiform avicu- 

 laria, one on either side a little proximal to the aperture, is characteristic 

 of this species. From 6 to 10 very slender marginal spines occur low 

 down around the distal end below the level of the aperture. 



The ovicell is slightly flattened above, situated on the distal side 

 of the peristome, hyperstomial and closed by the operculum. 



It is a circumtropical species, but has been noted on the Pacific coast 

 of the Americas only by Canu and Bassler from the Galapagos Islands 

 (also from Hawaii). 



Hancock Stations: Noted at 25 different stations from Santa Barbara 

 Island, Station 1064, off southern California to the Galapagos Islands. 

 Angel de la Guardia and San Esteban Islands in the Gulf of California ; 



