Phacussa.] UASTROFODA. 623 



slightly reflected ; eye-peduncles long and thick, tentacles moderate. 

 Jaw arcuate, with numerous imbricating vertical plaits which usually 

 denticulate the margins. Central and lateral teeth of radula tricuspid ; 

 marginal teeth with a long and oblique rnesocone, lacking side cusps. 



Shell depressed, umbilicated ; the spire convex, periphery rounded ; 

 whorls striate or with fine ribs ; the protoconch smooth ; aperture 

 rounded-crescentic ; peristome simple. 



Distribution. New Zealand and Tasmania. 



KEY TO SPECIKS. 



A. Shell narrowly perforate or imperforate. 



a. Small ; greatest diameter, 6J mm. ; about 8 riblets per milli- 

 metre . . . . . . . . kypopoliu. 



aa. Larger ; greatest diameter, 8 mm. or more. 



6. With fine thread-like growth-lines . . . . . . fulminatu. 



bb. With radial riblets, 4-5 per millimetre . . costata. 



B. Shell narrowly umbilicate. 



a. Riblets about 3 per millimetre, umbilicus one-sixth to one- 

 seventh of greatest diameter . . . . . . Henryi. 



ad. Riblets about 5-6 per millimetre, umbilicus about one-ninth 



of greatest diameter . . . . . . . . Helmsi. 



1. Phacussa fulminata, Hutton, 1883. Plate 50, fig. 1. 



Zonites (?) fulminata, Hutt., T.N.Z.I., xv, 1882 (1883), 138. Phacussa ful- 

 minata, Hutton, T.N.Z.I., xvi, 200 : Suter, P. Mai. 8., iii, pi. 15, f. 8 

 Heclley and Suter, P.L.S. N.S.W. (2). vii. 635 ; Suter, J. de Conch., xli' 

 244. 



Shell depressed, subperforate or imperforate, finely striated, with 

 numerous brown zigzag bands. Sculpture consisting of very fine hair- 

 like and flexuous growth-lines ; microscopically decussate. Colour 

 pale-horny, with numerous radial zigzag reddish-brown bands on 

 the body-whorl, winch show only as irregular radiating bands on 

 the spire-whorls. Epidermis thin, membranous, not shining. Spire 

 slightly convex, its height about half that of the aperture. Protoconch 

 of 1| flatly convex and smooth whorls. Whorls 5^ to 6, slowly increas- 

 ing, lightly convex, the last regularly rounded at the periphery ; base 

 flatly convex, somewhat depressed in the centre. Suture Avell im- 

 pressed, very narrowly margined below, .l/n'rhire, subvertical, trans- 

 versely Innately rotund. Peristome thin, regularly arched, sharp. 

 Columella short, vertical, arcuate. Inner lip callous, reflected, com- 

 pletely sealing up the narrow umbilicus in quite adult specimens. 



Diameter Ma]., 8-5 mm. ; ruin., 6-8 mm. : height, 5-8 mm. (type). 

 Diameter Maj., 11-5 mm. ; min., 10mm.: height. 7mm. (specimen 

 of 6 whorls). 



Dentition (Hutton. T.N.Z.I.. xvi, 173. pi. 10. f. J). Formula of 

 radula 20 + 18 + 1 + 18+20. Central tooth rectangular, the length 

 nearly three times the breadth ; the reflexed portion small, con- 

 stricted at the sides, the point small. Laterals bicuspid, the inner 

 cusp much larger ; inner laterals with the inner side emarginate. the 



