Septa.] GASTROPODA. 303 



short and truncated canal ; outer lip vertical, with an external varix, 

 thickened and crenated or denticulated internally ; columella ex- 

 cavated, slightly twisted below, inflected with the canal, surface 

 rough or smooth, with a parietal tooth bordering the posterior channel. 

 Operculum ovate, its growth annular either from a subapical or sub- 

 marginal nucleus. 



The Tritons are distinctly tropical in distribution, no species in- 

 habiting the colder seas. Fossil they appear first in the Cretaceous, 

 and numerous species occur in the Tertiary. 



A number of species have a world-wide distribution, which is 

 doubtless due to their free-swimming or pelagic larvae. These are 

 very different at first from the adult both in animal and shell, under- 

 going a metamorphosis at a period subsequent to hatching. 



Vernacular Name. Triton-shell. 



KEY TO SPECIES. 



. Shell with one varix only . . . . . . . . . . costata. 



fia. Shell with more than one varix. 



b. Spiral ribs broad, smooth, only those close to the suture 



nodulous ; interstices narrow . . . . . . tritonis. 



bb. Two spiral strongly nodulous ribs ; interstices broad, with 



fine spiral threads . . . . . . . . . . rubicunda. 



1. Septa rubicunda, Perry, 1811. Plate 1, fig. 3: Plate 43, fig. 1. 



Septa rubicunda, Perry, " Conchology," 1811, pi. 14, f. 4. Triton nodifer, 

 Lam., A.s.V., vii, 1822, 179. T. nodiferus, Lam., Man. Conch. (1), 

 iii, 10, pi. 1, f. 2, 3 : Conch. Icon., ii, pi. 3, f. 1). T. australe, Lam. : 

 Button, C.M.M., 13 ; M.N.Z.M., 63, not of Lamarck. Lotorium rubicun- 

 dum, Perry, Index, 75; Kesteven, P.L.S. N.S.W., 1902, 464, f. 2 in text 

 (protoconch). 



Shell large, fusiform, varices in the same direction on alternate 

 whorls, with nodular spiral ridges, whorls shouldered. Sculpture con- 

 sisting of strongly nodular spiral ribs, 2 on the spire-whorls, 8 pro- 

 minent spirals on the body-whorl, and numerous finer and closer 

 ones on the lower half of the base ; shoulder with a number of close 

 or distant subsequently strong spiral ridges, very little nodulous ; 

 interstices between the strong spiral ribs finely spirally striate ; varices 

 rounded on the spire-whorls, elevated and sharp on the body-whorl. 

 Colour yellowish-brown, variegated with dark brown and white on the 

 cinguli ; aperture white, teeth of the outer lip reddish-brown, inner 

 lip light brown, the plications white. Spire high, conical, usually 

 higher than the aperture. Protoconch of 3| whorls, semitransparent, 

 delicate pink, smooth, shining. Whorls about 10, distinctly shouldered, 

 with a nodular keel ; base convex, concave around the base of the 

 neck. Suture deep, uneven, and wavy. Aperture oblique, ovate, dis- 

 tinctly channelled above, with a short, open, and somewhat recurved 

 canal below. Outer lip expanded, sharp, denticulate, with an outer 

 varix, inside with long and strong teeth, sometimes arranged in groups 



