325 



Aperture regularly seiiiilunate, nearly erect ; outer lip thin ; 

 columella-margin thin, thinly and freely everted posteriorly, 

 joined by a callous film to the outer lip. Umbilicus wide, simple, 

 the ornament of the body-whorl entering the cavity. 



D linens io7ts. — Length, 18 '5 ; width, 18 ; diameter and radius 

 of aperture, 14 and 9 ; width of umbilicus, 3. 



Localities. — Eocene : Muddy Creek (rare) ! ; River Murray 

 Clifis (very rare)! ; Mornington! ; and Spring Creek (very rare)!. 



13. Natiea polita, Ttnison-Woofh. 



Proc. Roy. Soc. Tasm., for 1875, p. 23, t. 1, f. 4 (1846) (lig. 

 not good). 



Shell shining, moderately stout, ventricosely sub-globulose, 

 umbilicated. Whorls four and a-half, separated usually by a 

 profundly canaliculate suture. Aperture semilunate, slightly 

 oblique ; outer lip obtuse, not at all arched. Surface smooth or 

 transvel^sely finely striate, and faintly spirally lined. 



Dimensions. — The shell varies in the height of the spire, and 

 much in size ; an averaged sized specimen measures, long. 8-75, 

 lat. 7*5 to 7 "25, umbilicus 1. Some extremely low-spired forms, 

 with which is invariably associated an ill-defined channelled suture 

 and wider umbilicus (about 2 mm.), give the following measures: 

 — long. 8-5, lat. 9-5 (River Murray) ; 13-5 by 13-5 (Table Cape); 

 this variety which I will name injiata approaches in shape to 

 X. Hamiltonensis. 



Localities. — Forma typica, Eocexe : Table Cape ! ; Muddy 

 Creek, also as derived in the upper beds (Miocene) ! ; Morning- 

 ton ! ; Cheltenham ! ; Gellibrand River ! ; Belmont ! ; ■ River 

 Murray Cliff's ! ; Shelford !. Miocexe : Jemmy's Point (a single 

 dwarf ex.!). Forma injiata : Table Cape ! ; River Murray Cliffs ! ; 

 Fyansford ! ; Bird-rock Bluff (chiefly intermediate between forma 

 typica and var. injiata) ! ; Bellarine Peninsula ! . 



Remarks. — Tenison- Woods (Proc. Roy. Soc. Tasm. for 1877, 

 p. 32, 1878) records X. polita, also, as a recent shell on the 

 Tasmanian Coast. Johnston (id. for 1884, p. 221, 1885) 

 adduces the following distincti(jns for the separation of the living 

 analogue under the name of N. Beddoniei : — 



" In the living form the spire is more depressed, and the 

 whorls increase more rapidly in size. In the fossil form the 

 nucleus is invariably smaller than in the living representative, 

 and the number of whorls in mature specimens is four and a- 

 half. In the living mature form the number of whorls is 

 invariably three and a-half. The aperture in both does not 

 present any marked difference, if we except the fact that, in the 

 fossil state, the inner margin is almost vertical. In the living 

 form, the same feature is more decidedly angled relative to a 



