9i Transactions. — Zoology. 



at night-time I fouud all the animals In'glily phosphorescent. 

 The margin of the mantle showed a violet light, and this was 

 intensified by a touch with a needle. The secreted mucus 

 was also phosphorescent for some time. I do not know of any 

 other fresh-water shell showing this phenomenon, though it is 

 well known in many marine shells, especially in the P ho ladich,;. 

 It is very likely that the cells of Mueller, in connection with 

 the nervous system, produce this light. Having no material 

 at iny disposal for the time being, I have to postpone an 

 examination of the animal. It would be of interest to know 

 whether Laiia fluviatilis shows the same phosphorescent 

 pov.'er. 



Vitrinopsis (Vitrinoidea) dimidiata, Pf. 



This mollusc was first described by Pfeiffer (P.Z.S., 1851) 

 under the name of Vitrina dimidiata. There can be but little 

 doubt that Pfeiffer never saw the animal, but only the shell ; 

 otherwise this distinguished conchologist would at once have 

 seen that it differs widely from the genus Vitrina. Professor 

 F. W. Hutton, when undertaking the revision of our Land 

 Mollusca, for which splendid scientific work conchologists owe 

 him their gratitude, saw the error Pfeiffer had made and 

 created a new genus, Otoconcha (Trans. N.Z. Inst., xvi., 

 p. 199) for our mollusc. When I first found this slug in the 

 Forty-mile Bush it really puzzled me, but at last I found that 

 it agrees well with the description of the genus Vitrinoysis , 

 Semper (1870), a genus which was not known to Professor 

 Hutton at the time of his revision of our land-shells. Vitrin- 

 opsis was hitherto only known from the Philippine Islands, 

 where it was discovered by Semper. 



I will not enter into fuller particulars at the present, as I 

 expect to get some specimens of Vitrinopsis from the Philip- 

 pine Islands next year, thus enabling me to compare them 

 with our V. dimidiata and to give a complete record. 



Potamopyrgus corolla, Gould (viviparous). Plate XVIII. , 

 fig. 13, a, h, c. 



A short time ago I had the chance of making a highly in- 

 teresting observation on the propagation of the above-named 

 juollusc. I kept a number of specimens alive in a glass tube, 

 and, on examining it, I found to my great astonishment sixteen 

 very minute white young molluscs crawling about on the glass. 

 (This was on the 6th of October, and the animals were put in 

 the glass. tube on the oth.) There was no trace of eggs to be 

 seen, and, as I observed on tlie following days, when some more 

 young animals appeared, our P. corollai^ viviparous; and it is 

 to be expected that our other species of the genus, as well as 

 those in Tasmania, will show the same mode of propagation. 



