86 CRITICAL OBSERVATION'S ON RECENT CONTRIBUTIONS, ETC. 



Witli respect to the genus Bithynella, I particularly noted 

 that the species vary widely with the slightest difference m 

 the conditions of their environment. In my notes I showed 

 that the degree of brackishness had a very marked effect. 

 The variety then known as B. imkarinata, T. Woods, in the 

 drain near the Railway Station, Launceston, partly influenced 

 by the tidal waters of the Tamar, has six whorls, shell 

 moderately thick, coated with reddish decomposed confervK. 

 About a mile distant, where the water is still more brackish, 

 the shell of the same species is of a very delicate pale horn 

 colour, transparent, six whorls, and scarcely half the size of 

 the individuals in the habitat previously mentioned. The 

 carina of epidermal membrane, at that time deemed to be of 

 specific value, was observed to be very inconstant, sometimes 

 in awl-shaped spines, as in B. Legrandia?ia, Brazier ; in inter- 

 rupted lines, as in Bithynella 7inicarinata ; in continuous lines 

 simple ; in continuous or interrupted lines fimbriated ; and 

 most frequently without any apparent carina, as in Paliides- 

 irina Wiscmaniana^ Brazier, or its synonym BWiyjiella 

 Tasmaiiica, Ten. Woods. Nor was my attention confined to 

 the exo-skeleton. The malacological character of the animals, 

 including the odontophore, were frequently examined by me 

 under the microscope, and careful drawings were made of the 

 various parts. Descriptions of the animal and its dentition 

 and external characters were given in my paper, together 

 with similar descriptions of several interesting new forms not 

 previously observed. Lithographs of these drawings were 

 prepared at the same time, l)ut these came to hand too late 

 to be inserted in the proceedings along with the paper. 

 These lithographic sheets, however, were preserved, and I 

 now present them as an accompaniment to these notes. The 

 following is a list of the species then described for the first 

 time : — 



Gundlachia Petterdi, Mihi. 



Amnicola Launcestonensis, Mihi. 



Planorbis Atkinsoni, Mihi. 

 Scottiana, Mihi. 



Pomatiopsis Badgercnsis, Mihi. (fossil) 



Ancylus Woodsii, varieties A., B., Y., Mihi. 



Bithynella nitida, Mihi. (fossil) 

 With the necessary exception of the fossil forms, the mal- 

 cological characters of all these species were observed and 

 described in addition to those of various fonns of Bithynella 

 and Physa Tastiianica, T. Woods. 



So far as I am aware, these were the first descriptions pub- 

 lished of the malcological characters of Tasmanian fresh 

 water shells. 



I claim no special credit for tliis, because with the eiceptioD, 



