12 FLAMMULINA. 



The following sectional or subgeneric divisions may be distin- 

 guished : 



Phacussa Hutt., p. 12. Phenacohelix Sut., p. 16. 



Thalassohelix Pils., p. 12. Flammulina Mart., p. 17. 



Gerontia Hutt., p. 14. Suteria Pils., p. 17. 



Allodiscus Pils., p. 14. Hedleyoconcha Pils., p. 18. 



Pyrrha Hutt., p. 15. Monomphalus Anc., p. 19. 



Therasia Hutt., p. 15. B-hytidopsis Anc., p. 20. 



Subgenus PHACUSSA Hutton, 1883. 



Phacussa HUTTON, Trans. N. Z. List, xv, p. 138 (proposed for 

 Zonites (/) helmsi 8&d fulminata.) 



Shell depressed, umbilicated ; the spire convex, periphery 

 rounded. Whorls striate or with fine ribs, the apical H whorls 

 smooth. Aperture rounded-crescentic, peristome simple. Type F. 

 helmsi Hutt. (pi. 3, figs. 10, 11, F. hypopolia Pfr.) 



Animal elongated ; fyot very narrow and long, compressed, not 

 tapering, truncated posteriorly and with a caudal gland ; mantle 

 slightly reflected ; eye peduncles long and thick, tentacles moderate 

 (Hutton, Ph. helmsii.) 



Jaw arcuate, slightly tapering toward the ends, with numerous 

 flat imbricating vertical plaits (20-25 in helmsi, about 45 in hypo- 

 polia) which denticulate the margins (pi. 2, figs. 2, 3, F. hypopolia.) 



Dentition : About 110 nearly straight transverse rows of 15-11- 

 1-11-15 to 17-13-1-13-17 teeth. Central tooth with a wide meso- 

 cone and minute ectocones. Lateral teeth tricuspid, the entocone 

 minute, obsolete on the outer ones. Marginal teeth having the basal- 

 plate subquadrate, mespcone very long and oblique, lacking side 

 cusps (pi. 2, fig. 1, F. hypopolia.) 



Distribution, New Zealand. The shell in this group is very similar 

 to that of Phenacohelix, but the marginal teeth lack side cusps, the 

 mesocone being strongly developed, giving it a Zonitoid aspect. 

 F. helmsi Hutt. F. hypopolia Pfr. ii, 181. 



v. maculata Hutt. F. fulminata Hutt. 



Subgenus THALASSOHELIX Pilsbry, 1892. 



Thalassohelix PILS., The Nautilus, Sept. 5, 1892, p. 56, type H. 

 zelandice (Gray) Hutton. Thalassia of HUTTON and other New 

 Zealand authors. Not Thalassia ALBERS, Die Hel. 1860, p. 59- 

 Not Thalassia Chevrolat, 183-J, a genus of Coleoptera.. 



Shell umbilicated, thin, depressed or trochiform, the periphery 

 acutely keeled (zelandur), bluntly angled (obiinbila), or rounded 



