238 PLANAXIDJE. 



Section HOEA, Gray, 1847. 



Shell smooth, covered by an epidermis ; whorls flattened ; outer 

 lip thick, sillonated within. P. BRASILIANUS, Lam. 



Subgenus QUADRASIA, Crosse, 1886. 



Shell smooth, spirally striated, imperforate ; peristome thickened, 

 the margins joined by a strong parietal callus, columella dilated 

 with a rounded obtuse tubercle at the base, base of aperture emar- 

 ginate. Operculum thin, corneous, paucispiral, the apex almost 

 terminal. Fluviatile. Q. HIDALGOI, Crosse. 



Philippines. 



Perhaps more nearly related to Melanopsis. 



Subgenus QUOYIA, Desh, 1830. 



Conically elongated, apex decollated, whorls solid, flattened, 

 spirally striated, mouth notched in front, grooved within, columella 

 smooth, truncate in front, with a posterior spiral plication. 



P. DECOLLATUS, Quoy. 



Fissilabra, Brown, 1836, and Leucostoma, Swains, 1840, are syno- 

 nyms. 



Subgenus HOLCOSTOMA, H. & A,, Adams, 1853. 



Shell thin, covered with a bristly epidermis, aperture with a 

 posterior produced canal, with an anterior sinus, columella concave, 

 with a posterior callus. P. PILIGERUS, Phil. 



Indian Ocean. 

 Litiopince. 



Genus LITIOPA, Rang, 1829. 



Shell minute, conoidal, columella truncate at the base, outer lip 

 simple, thin, notched in front. Operculum spiral. 



Animal (PI. 40, fig. 79) with three cirriform filaments on each 

 side, operculigerous lobe with two posterior appendices, no siphon. 



To ascend through the water this little pelagic animal emits an 

 air bubble enclosed in a glutinous secretion, which draws out a 

 thread as it rises, and finally attaches itself to floating sea weed. 

 Bombijxinus, Belanger, 1834, is a synonym. L. MELANOSTOMA, 

 Rang. 



Subgenus ALABA, A. Ads., 1862. 



Shell ovate-conical or elongated, subdiaphanous, whorls plicate 

 or varicose, apex submammillate, columella often truncated, oper- 



