Acmcea.] 



GASTROPODA. 



63 



AA. Shell smooth to the naked eye, sculpture more or less micro- 

 scopic. 



o. Shell small, whitish, with 10 radiate pinkish rays . . roseoradiata. 



aa. Shell small, laterally compressed, navicular, brown . . scapha. 

 aaa. Shell usually larger, variegated. 



6. Shell flattened, membranaceous, with concentric 



brown and white or greenish bands . . . . jragilis. 



c. Shell thin, pellucid. 



d. Surface painted with a brown network . . dcedala. 

 dd. Whitish, with brown radiate lines . . subtilis. 



cc. Shell more solid, not pellucid. 



d. Shell rather large, length to 30 mm., apex 

 anterior, but sometimes removed to 

 anterior fourth . . . . . . pileopsis. 



dd. Shell smaller, not exceeding 20 mm. in 



length. 



e. Apex mostly anterior, sharp and 

 hooked, black, tessellated and 

 blotched with white . . . . cantharus. 



ee. Shell high and rounded or couoidal. 

 /. Central area variegated with brown, 



sometimes nearly white . . parviconoidea. 

 //. Central area purplish-black, more 

 or less distinctly stellate ; 

 young shell white, with a 

 central black star . . . . nigrostella. 



eee. Conoidal, with numerous radiate black 

 rays. Interior bluish-white, spa- 

 tula white, with a few brown spots, 

 border yellow, with brown rays- . . Helmsi. 



Subgeii. 1. ACM.EA, s. str. 



Muzzle with lappets, no marginal teeth. Formula of teeth of 

 ladula : 2 (1 + Oxl) 2. 



1. Group o] Acmaea cingulata. 

 Teeth of radula typical, with short, rounded cutting-points. 



1. Acmaea cingulata, Hutton, 1883. Plate 5, fig. 6. 



Acmcea cingulata, Hutton, N.Z.J.S., i, 477 ; T.N.Z.I., xvi, 215 ; Man. 

 Conch. (1), xiii, 53 ; P. Mai. S., vii, 316, pi. 27, f. 3-5. 



Shell oval, conoidal, moderately solid, white to yellowish-brown, 

 with numerous radiating ribs, which are low, rounded, and varying in 

 number from 30 to 50 ; there are usually 10 to 15 primary ribs, and 

 numerous finer riblets in the interstices ; a number of concentric 

 ridges sometimes render the ribs slightly crenate. Colour mostly 

 white, sometimes light brown, the ribs nearly white. Apex at the 

 anterior fourth, oval in shape and convex, mostly dark brown ; 

 .anterior slope nearly straight. Inside white, porcellanous, central 



