318 GASTROPODA. [Pectinibranchia. 



Genus 3. OMALAXIS, Deshayes, 1830. 



Omalaxis, Desh., Encyclop. Meth., Tabl., 1830. Type : Solarium bifrons, 

 Lam. Omaloxon (Desh. em.), Agassiz. Omalaxon (Agass. em.), Herr- 

 mansen. Omalalaxis (Desh. ?), Herrmansen. Bifrontia, Deshayes, 1832. 

 Orbis, Lea, 1833. Homalaxis (Desh. em.), Fischer, 1885. Homalaxon (as 

 of Agassiz), Watson, 1886. Not Omalaxis, Tryon, Syst. Conch., ii, 219. 



Shell subdiscoidal. flat or slightly concave above, whorls carinated 

 at the periphery, the last sometimes detached from the others ; peri- 

 stome not continuous ; umbilicus wide and deep. Operculum circular, 

 multispiral. 



Only few species are known New England, Brazil, Australasia. 



Fossil. Tertiary. 



1. Omalaxis amoena, Murdoch and Suter, 1906. Plate 15, 



figs. 21, a, b. 

 Omalaxis amoena, M. & S., T.N.Z.I., xxxviii, 1905 (1906), 293, pi. 24, f. 30-32. 



Shell small, discoidal, bicarinate, beautifully sculptured, sides 

 straight but oblique, umbilicus wide, carinated, perspective. Sculp- 

 ture : Upper side with a beaded cord on each side of the suture, the 

 outer one being more prominent ; between them are 3 fine elevated 

 spiral threads, the whole crossed by numerous oblique elevated radiat- 

 ing ridges, with equal interspaces, which continue over the periphery 

 to the basal cord ; on the periphery is a third beaded and conspicuous 

 cord, which is buried in the suture ; still another marginates the base, 

 and between them are 3 small spiral ridges ; between the basal and 

 umbilical ribs is a small beaded spiral, the whole reticulated by some- 

 what irregular distant radiate ribs, interstices having now and again 

 one or more fine ridges ; the umbilical rib distinctly beaded. Colour 

 white. Spire flat. Protoconch dextral, smooth, consisting of 1J con- 

 vex whorls. Whorls 3. flattened, regularly increasing, with the 

 sides almost straight, subquadrate in section, the base somewhat 

 excavated. Suture slightly channelled. Aperture subquadrate. Outer 

 lip sharp, with 2 angles above and 1 below. ColumeHa short, concave. 

 Umbilicus large, scalar, with the sides inclined. Operculum unknown. 



Diameter Maj., 3 mm. ; min., 2-5 mm. : height, 1 mm. 



Type in the Dominion Museum, Wellington. 



Hob. Off Great Barrier Island, in 110 fathoms (one dead shell). 



Remarks. This species is almost identical with DiscoJ/elix retifera, 

 Dall, from the Pliocene of Florida. A similar form. 0. meridionalis, 

 Hedley, was dredged in Port Stephens, New South Wales, but it is 

 not so elaborately sculptured. 



Fam. EPITONIIDjE. 

 Scalariidce. Scalidce. 



Animal having a retractile proboscis ; tentacles close together, 

 long and pointed, the eyes on slight elevations near their outer bases ; 

 mantle-margin simple, with a rudimentary siphonal fold ; foot trun- 



