BY W. F. PETTERD. 63 



and the other lives oii the surface of mud, within the influence 

 of the tide. 



In the Physce a large amount of work remains to be done, 

 so as to arrange the species with satisfaction, and no doubt 

 many of the fonns described as distinct species, will require 

 reduction. Their investigation and determination has been 

 difficult wherever undertaken. In the genus Planorhis there has 

 also been some little confusion, for I find upon the examina- 

 tion of typical specimens, that the P. meridionalis, Br., is very 

 distinct from the shell named by the Kev. Tenison-Woods, as P. 

 Tasmanica, which name was withdrawn by that learned gentle- 

 man in favour of the former, under the supposition that they 

 were identical. An examination of the drawings — taken 

 from undoubted typical examples — will at once show the great 

 amount of difference in form, and a careful investigation of 

 many hundreds of specimens has not resulted in the finding 

 of any intermediate variations, so that I consider that both 

 species should be retained. That described by Mr. R. M. 

 Johnston under the name of P. Athinsoni, I find to differ 

 very materially fi-om either, although it clearly shows a nearer 

 approach to the P. Tasmanica, than to P. meridionalis. 

 Another, but smaller form, will be given in the catalogue, it 

 is the P. Scotiiana, a shell of very constant chai'actcr, with- 

 out any likeness to the throe species mentioned. In the 

 Ancyllnce but little remains to be done, although I have 

 examples from the Liffey and Scamander rivers that differ 

 very much from described species. We have two remai'kably 

 large species, one of which, i\\Q Ancijlus Cumminrjianus, Bor., 

 forms the typo of the genus Cnmminrjia, established by 

 Closson, for its reception ; this was proposed many years ago 

 by Hanley. The animal of this shell, as well as that of its 

 congener, A. Irvince, mihi, will repay examination ; a dis- 

 tinguished American conchologist thinks they will show a wide 

 departure from tbat of the typical Ancylince. Two additional 

 species of Assiminea have been recently added to our fauna, 

 one an Australian form, and tne other, so far as at present 

 known, restricted to a single locality on the North Coast. 

 The liissoa marioi of Touison- Woods presents the form of 

 Hydrobia, and Professor Tate is of oi>inion that it would be 

 better placed in that genus, in which I think it will be also 

 necessary to place tlie Rissoa Brazicri, T. Woods ; the lial)it of 

 the latter is much the same as typical Hydrohiw, but an 

 investigation of the animal in both cases would be of some 

 importance, and moreover settle the point. In the genera 

 Pisidium and Spliarium some little difficulty will be 

 encountered, and it may be necessary to add a new species to 

 each. The S. Tasmanicum will require careful comparison 

 ■with examples of British species, as it may prove to be an 

 acclimatised form. 



