290 allan hancock pacific expeditions vol. 14 



Key to the Genera of Petraliidae 



1. Zooecia very large, more than 1 mm long; peristome high and 



flaring; a large dorsal pore present Coleopora 



Only moderately large, peristome low 2 



2. Dorsal surface with several scattered attachment 



tubules Robertsonidra 



No dorsal attachment tubules 3 



3. Aperture nearly round, ovicell surrounding the 



aperture Cycloperiella 



Ovicell not enclosing the aperture 4 



4. Aperture with the proximal border transverse .... Petralia 

 Aperture with a large arcuate poster Hippopodina 



Genus PETRALIA MacGillivray, 1879 



Ovicell hyperstomial, closed by the operculum, deeply immersed. 

 Poster wider than the anter. The shield is a regular smooth pad around 

 the aperture; it bears sometimes two small lateral avicularia. (After 

 Canu and Bassler, 1929:253.) Genotype, Petralia iindata MacGillivray, 

 1869. 



Petralia japonica (Busk), 1884 

 Plate 31, fig. 5 



Lepralia japonica Busk, 1884:143. 



Petralia japonica, Canu and Bassler, 1929:254. 



Without the ooecium it is not possible always to distinguish the genus 

 Petralia from Petraliella Canu and Bassler. The present small fragments 

 resemble exactly Canu and Bassler's figure 1, Plate 23 (1929), except 

 for the lack of ovicells. The aperture is broadest proximally, the proximal 

 border is slightly arcuate, the circumoral shield is low and broad and 

 bears on either side of the aperture a small avicularium with a short 

 triangular or somewhat semicircular mandible, the rostrum elevated. 

 The frontal is coarsely perforate and somewhat roughened by heavy 

 calcification. 



The species is widely distributed in the western Pacific and Indian 

 Oceans, but has not been noted along the American coasts. 



Hancock Stations 468-35, Port Parker, Costa Rica, 5 fms, and 303, 

 Port Culebra, Costa Rica, 17 fms. 



