Sutek. — Species of the Genus Isidora. 



275 



Fig. 7- 



Isidora lirata, T. Woods, subsp. conferta, n. subsp. 



Shell globosely ovate, sinistral, corneous-translucent, thin, 

 almost imperforate, the columellar reflexion leaving only a narrow 

 chink. The distant lines of growth are rather regular, especially 

 on the upper whorls, and under the lens fine regular and close 

 spiral lirse are visible. The colour varies from very light horny to 

 light olive-brown. The spire is short, about one-third the length 

 of the shell. The pullus is acuminate, of darker colour, con- 

 sisting of two whorls with fine incremental striation. There are 

 four whorls, either strongly shouldered or having only 

 a posterior angle, which usually gets lost on the 

 body-whorl ; the latter is forming the greater part 

 of the shell. The base is convex, the suture im- 

 pressed. Aperture vertical, elongately oval, acu- 

 minate above and produced anteriorly. The outer 

 lip is regularly rounded, sharp, thin ; the inner lip 

 is twisted, forming a distinct fold near the axis of 

 the shell ; not much reflexed. Fig. 7 represents 

 a distinctly shouldered form, and fig. 8 with only 

 a slight angulation on the whorls. 



This subspecies is distinguished from the 

 species by its ventricose form and the much 

 broader aperture, approaching T. tabulata, Gould. 



I have specimens from two localities : — 

 (1.) From swamps near Otorohanga, King- 

 country. These are strongly keeled (fig. 7). 

 Three specimens were measured — Shell : length, 



II mm. ; breadth, 7 mm. Aperture : length, 

 7 mm. ; breadth, 4 mm. Shell : length, 9^ mm. ; 

 breadth, 6| mm. Aperture : length, 6^ mm. ; 

 breadth, 3| mm. Shell : length, 9 J mm. ; breadth, 



Aperture : length, 6 mm. ; breadth, 3J mm. The mean 

 rationis are — i. = 1 : 16 : ii. = 1 : 1*7 ; hi. = 1:16. 



(2.) From Wairau Kiver, south of Birch Hill Station, Nelson. 

 These specimens are much lighter in colour, the upper whorls 

 slightly angled (fig. 8). Three specimens were measured — Shell : 

 length, 11-12 mm. ; breadth, 7— 7-J mm. Aperture : length, 

 breadth, 4| mm. The mean proportions are — 

 1:1-6; ii. = 1 : 1'9 ; hi. = 1 : 1"4. The means for the two 

 localities are— i. = 1 : 1*6 ; ii. = 1 : 1*8 ; hi. = 1:15. 

 Type in my collection. 



To repeat, the following species are omitted : — 

 (1.) Physa variabilis, Gray, insufficiently described and un- 

 figured. 



(2.) Physa gibbosa, Gould, inhabits Australia. 



6 mm. 



8-8| mm . 



i. 



