252 Transactions. — Zoology. 



figured by Hutton. The number of laterals and marginals is 

 very variable, and the figures sufficiently show the different 

 arrangements of the cutting-points on the transitional teeth. 



Sub-fam. PLANORBIN^E. 



Genus Planorbis (Guett.), Geofiroy (1767). 

 Planorbis (Gyraulus) corinna, Gray (1850). 

 P.Z.S., 1849. p. 167 (1850). 



Lake Waikare (Stat. 33 — Obtained by netting in weeds). — One 

 specimen only was found, which has three whorls and a diameter 

 of 1\ mm. 



Genus Isidora, Ehrenberg (1831). 



Isidora tabulata, Gould, subsp. moesta, H. Adams (1861). 

 P.Z.S., 1861, p. 144. 



(1.) Lake Waikare (Stat. 19 — From reeds). — One specimen 

 only was obtained. It is of light-horn colour, very thin, covered 

 with a greenish coating ; there are four whorls, the last two 

 distinctly shouldered and keeled. Columella excavated in the 

 middle, fold distinct, reflection of columellar lip small ; outer lip 

 sharp, regularly arched. It is a little more slender than the 

 type. Shell : length, 7 mm. ; breadth, 4 mm. Aperture : height, 

 5 mm. ; breadth, 2 J mm. Ratios : i. = 1 : P75 ; ii. = 1 : 2 ; 

 iii. = 1 : 1*4. (The ratios are the same as in the revision of 

 Isidora.) 



(2.) Lake Waikare (Stat. 28 — From weeds in water from 

 H ft. to 2 ft.). — Two specimens of dark-brown colour, solid and 

 large, keeled, the keel becoming obsolete on approaching the 

 aperture ; columella twisted. They differ but little from the 

 type. Shell: length, 17 J mm. ; breadth, 11mm. Aperture: 

 height, 11mm.; breadth, 6 mm. Shell: length, 14 mm. ; 

 breadth, 9 J mm. Aperture : height, 10 mm. ; breadth, 5 mm. 

 Ratios : i. = 1 : 1-6; ii. = 1 : 1-8; iii. = 1 : 1-6. i. = 1 : 1-5; 

 ii. = 1 : 2 ; iii. = 1 : P4. The accompanying fig. 15 shows 



@. — ^ . — -, ^ — ■* some teeth of the radula, 

 \\d LJj <^f t^j^ which need no explanation. 

 V^ 1"? 16 m r ^^ ie dentition of our forms 



P .r of Isidora is so variable that 



*°" I doubt whether it can be 



used as a help to separate the species. However, a consider- 

 able number of animals of each species has to be examined 

 before this point ran l»e settled definitively. 



(3.) Lake Waikare (Stat. 28f — From weeds in water from 

 1 1 Ii. to 2 ft.). — Two " dead shells," one young, the other nearly 

 adult. They resemble those from the last station, but are a 

 little more wntricose, and have the spire a little shorter. Shell: 



