232 GASTROPODA. [Pectinibranchia. 



elevated conical, acute, outlines slightly convex. Protoconch minute, 

 sharp. Whorls 6, regularly increasing, convex, rounded or shouldered, 

 with or without spines ; base convex. Suture not deep. Aperture 

 ovate, subangled above. Peristome continuous, thin and sharp, with 

 a very thin inner callosity. Columella arcuate, thin, very little ex- 

 panded. Operculum normal. 



Diameter, 2 mm. ; height. 5 mm. (type). Ratio of D : H= 1 : 2-5. 

 The usual dimensions are 2-5-3 mm. by 5 mm. 



Dentition. Hutton, T.N.Z.I., xiv, 145, pi. 1, f. F. 



Type in the U.S. Nat. Museum, Washington. 



Hob. South Island of New Zealand, in lakes, rivers, and creeks. 

 The type is from Banks Peninsula (Pickering). 



Remarks. The species attains a very large size, 4 mm. by 8 mm., 

 in Lake Te Anau, and somewhat smaller in Lake Wakatipu, in depths 

 from 20 ft. to 300 ft. Specimens of a very light brown colour have 

 been found some years ago in meters connected with artesian wells at 

 Suniner, near Christchurch. 



3. Potamopyrgus corolla, Gould, 1847. Plate 13, fig. 24. 



Mdania corolla, Gld., P. Bost. S.N.H., ii, 1847. 223. Melanin corolla. Old., 

 Conch. Icon., f. 366. Amnicola corolla, Gould, I'.S. Expl. Ex.. xii. 129, 

 pi. 9. f. 149, a c. Pahtdestrina Cumingiana, P. Fisdi., J. de Conch., 

 1860, 208, pi. 4. f. 7. Hydrobia Crossei, Frfld., V.Z.B.G. Wieii, 1865. 

 595. Bythinella corolla, Gld. : T. -Woods, P.L.S. N.S.W., iii. 135, 

 pi. 13, f. 2, 3, 5. Hydrobia corolla, Hutt., M.N.Z.M., 83. Potamo- 

 pyrgus Cumingiana, Fisch. : Hutton, T.N.Z.I., xiv. 144. pi. 1, f. A. F. 

 P. corolla, Gld. : Suter, T.N.Z.I.. xxxvii. 260. 246. 



Shell small, ovate-conic, ventricose. thin, subpellucid, spinous, 

 angulate espinous, or smooth and rounded. Sculpture, if present, 

 consisting of numerous spines on a carina encircling the whorls a 

 little above the periphery, 17-20 on the last whorl ; they are long, 

 rather distant, curved, directed upward ; the first 3J whorls have no 

 spines ; sometimes there is only a black thread present, or the whorls 

 may be rounded and smooth. Colour light-yellowish, often covered 

 with a black coating. Epidermis thin, slightly shining in some speci- 

 mens. Spire elevated conic, a little higher than the aperture, out- 

 lines straight. Protoconch small, acute, of about 2 convex smooth 

 whorls. Whorls 6^, shouldered or rounded, the last large and some- 

 what swollen ; base convex. Aperture ovate, oblique, angled above. 

 Peristome continuous, strengthened by a white inner callus. Columella 

 arcuate, very little reflexed. Operculum horny, subspiral. 



Diameter, 4-5 mm. ; height, 6-5 mm. Ratio of D : H == 1 : 1-44. 



Dentition. Hutton, T.N.Z.I., xiv, 144, pi. 1, f. E. 



Type in the U.S. Nat. Museum, Washington. 



Hab. North Island of New Zealand, in lakes, rivers, and creeks ; 

 Chatham Islands. 



