Trochm.} GASTROPODA. 113 



on the funnel side, and a long fold transversely wound over the anterior 

 end and passing into the shell. False umbilicus deep, funnel-shaped, 

 contracted at the margin by a spiral rib with occasional tubercles. 



Diameter, 7-5 mm. ; height, 5 mm. 



Type in Mr. W. H. Webster's collection. 



Hob. Takapuna, in shell-sand. 



Remark. The shell has a close resemblance to the Victorian 

 C. plebejus. (Hedley.) 



Genus 2. MONODONTA, Lamarck, 1799. 



Jlonodonta. Lam., Mem. Soc. Hist. Nat.. 1799, 74. Type : M. labio, L. 

 Manodonio, Lam. : Ad., G.R.M., i, 417 ; Man. Conch. (1), xi, 8, 86. Labio, 

 Oken. Lehrbxich, 263. Monodontes, Montfort, Conch. Syst., ii, 195. 

 Trocliidon, Swainson, Treat. Malac., 351. Odontis, Sowerby, Cat. 

 Tankerville Coll., 53. Trochulus, Humphrey. Monodon, Schweigger 



Animal having long tentacles and 4 pairs of epipodial cirri. The 

 radula has the formula ool.5+l + 5.1oo. The prominent character 

 of the dentition is the development of the lateral basal angles of the 

 central and lateral teeth into broadly projecting lobes imbricating 

 over the adjacent tooth ; the cusp of the central is wide, shortly 

 reflexed, its edge denticulate at the sides, smooth in the middle. 



Shell imperforate. turbinate, ovate or globose-depressed, the peri- 

 phery rounded ; surface smooth or spirally ridged ; cqlumella simple, 

 arcuate, and spread upon the base at its insertion, below tubercu- 

 late, swollen, ending in a tooth, or simple ; outer lip smooth or lirate 

 within. 



With the exception of several forms from the west coast of South 

 America, the species are all Old World in distribution, mostly tropical. 



Geologically, the genus dates from the Trias. 



Subgen. 1. DILOMA, Philippi, 1845. 



Diloma, Phi]., Abbild., &c., i, 1845, 168. Type : Turbo nigerrimus, Gmel. 

 Shell globose or depressed conic ; aperture large, very oblique ; 

 columella not prominent, flattened, not cylindrical, generally con- 

 cave, arcuate, and slightly denticulate at the base, or smooth. 



Sect. 1. DILOMA, s. str. 

 Diloma, Phil., Ad. G.R.M., i. 419 ; Man. Conch. (1), xi, 9, 96. 



Shell globose, depressed or conic, imperforate, black ; smooth 

 or spirally grooved ; columella wide, concave, porcellanous ; lip mar- 

 gined with an iridescent band, which extends across the parietal wall. 



Diloma has been restricted by Fischer to the South American 

 species, but two are found on the coasts of New Zealand. The only 

 diagnostic character separating these from the other Australasian 

 forms is the band of nacre extending across the parietal wall, con- 

 necting the terminations of the peristome. 



