GASTROPODA. t)49 



Genus 5. THERMIA, Hutton, 1904. 



Thermiu, Hutt., P.L.S. N.S.W., xxix, 1904, 461. Type: T. Cressida, 

 Hutton. Pyrrha, Button, T.N.Z.I., xvi, 1884, 200; Pilsbry, Man. 

 Conch. (2), ix, 15 ; not of Cabanis, 1849, in Aves. 



Animal heliciform, mantle subcentral, reflected over the peristome 

 with an even margin ; tail truncate, with a large papilla and mucous 

 gland. 



Jaw arcuate, flatly plaited. 



Dentition : Central tooth with the mesocone only developed. 

 Laterals bicuspid, the entocones suppressed. Marginal teeth with 

 several cusps. 



Shell depressed globose, thin, translucent, striated and sometimes 

 minutely reticulated, imperf orate or narrowly umbilicated ; peri- 

 stome simple. 



Distribution. New Zealand. 



KEY TO SPECIES. 



A. Shell striately plaited, no distinct riblets. 



a. No distinct microscopic spiral striae ; whorls oi ; perfora- 

 tion closed, or only a little uncovered ; shell large, 

 12] mm. by 8 J mm. .. .. Cressida. 



act. Microscopic spiral strife very distinct ; whorls 4^ ; per- 

 foration only half-covered ; shell smaller, more de- 

 pressed, 9 mm. by 5-5 mm. . . . . . . virescens. 



B. Shell distinctly ribbed, 10 riblets per millimetre. 



a. Protoconch microscopically spirally striate ; spire about 

 two-thirds the height of aperture ; whorls 4J, sub- 

 angled ; perforation narrow, open ; shell small, 2'9 mm 

 by 2 mm. . . . . expedition^. 



aa. No microscopic spiral strife ; spire about half the height 

 of aperture ; whorls 5, distinctly angled ; perforation 

 nearly or quite covered ; shell larger, more depressed, 

 8i mm. by 5| mm. . . . . . . . . subincarnata. 



1. Thermia Cressida, Hutton, 1883. Plate 50, fig. 6. 



Pfeifferia (?) Cressida, Hutt,, N.Z.J.S., i, 1883, 476 ; T.N.Z.I., xvi, 178. 

 Pyrrha Cressida, Hutt., i.e., 200. Gerontia (Pyrrha) Cressida, Hutt. : 

 Pilsbry, Man. Conch. (2), viii, 72. Flammulina (Pyrrha) Crvssida, Hutt. : 

 Pilsbry, I.e.. ix, 15, pi. 3, f. 17-19. P//rrha Cressida, Hutt. : Hedley 

 and Suter, P.L.S. N.S.W. (2), vii, 640. Flammulina (Pyrrha) Cressida, 

 Hutt. : Suter, J. de Conch., xli, 248. 



Shell turbinate, depressed, very thin and fragile, translucent, 

 umbilicus covered. Sculpture formed by irregular, obliquely re- 

 tractive, somewhat sinuous striae and plaits, sometimes with a few 

 distant faint spiral lines. Colour fulvous or olive-horny. Epidermis 

 thin, shining, transparent. Spire convex, half the height of the 

 aperture. Protoconch of If flatly convex and smooth whorls. Whorls 

 5|, slowly increasing, rounded, periphery of last whorl slightly angled ; 

 base convex. Suture impressed. Aperture slightly oblique, lunately 

 rotund. Peristome thin and sharp, regularly arched. Columella ob- 

 lique. Inner lip slightly thickened and reflexed over the perforation, 



