ADDENDA ET CORRIGENDA. 



Since the completion of the printing of this memoir, Mr. 

 Tryon, in his " American Journal of Conchology," Yol. I, p. 220, 

 July, 1865, has proposed a new genus of Hydrobiina? under the 

 name of Gabhia, with the following diagnosis : " Shell like 

 Amnicola, Gould and Hald. Operculum paucispiral, calcareous. 

 Station, fresh water." The only species, G. australis, Tryon, is 

 new, and figured on pi. xxii, of the volume quoted (fig. 7). It 

 is from New South Wales. I have no opportunity to examine 

 this shell, but must remark that the characters given in the 

 desci'iption do not serve to distinguish it from the immature state 

 of Stenothyra in which the contraction of the aperture has not 

 yet commenced. The figure reminds us of Bythinia rather than 

 any other genus, for in it the operculum is represented as de- 

 cidedly concentric, although said to be "paucispiral" in the 

 description. 



• 



Ou page 12, line 4, after ^'Somatogijnis, Gill," add "Cochliopn, Stm." 

 The figure of Somatocjyrus isogonus, on page 22, is accidentally defective 

 in representing the lower extremity of the aperture as notched. 



August, 1865. 



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