FEESHWATEE STIELLS OF ATJSTEALIA. 295 



Spire sunken a little below the last wliorl. Volutions 4, equally 

 convex above and beneath ; the last in adult specimens carinated, 

 not verj acutely, a little below or at the middle. Lower surface 

 sunken in the centre about as much as the upper. Aperture 

 almost horizontal. 



Greatest diameter 5 millim., height 1|. 



Hah. Freshwater lagoons, Point Smith, Port Essington {Brit. 

 Mus.). 



This species is flatter than P. Gilherti, has no spiral striation, 

 is not so much sunken beneath, and the whorls have no indication 

 of the feeble angulation observable in that species. 



104. Plajstoebis macqtjaeiensis, n. sp. (Plate VII. figs. 4-G.) 

 Shell smaller than P. essingto7iensis , not quite so compressed, 



more sunken in the umbilical region, less acutely keeled and cor- 

 neous. Whorls 3-^. Aperture not so narrow perpendicularly as 

 in the above-named species, and scarcely as horizontal. 



Greatest diameter 4-|- millim., height l-L. 



Rah. Macquarie Eiver, New South "Wales {Bev. D. Lands- 

 horougTi). 



This species is smaller than P. Gilherti, has, no faint angulation 

 on the lower side of the last Avhorl, is a little less acutely keeled, 

 and has not spiral striae. 



105 . Plakoebis obtustjs, BesJiayes. 



Planorbis obtusus, Besli. MS. Mus. Cuming; Sowerby, Con. Icon. 

 fig. 39 a-b. 



Eah. Adelaide {Mus. Cuming). 



Although stated by Sowerby to be described in the Proc. Zool. 

 Soc, I have searched in vain for any description of this species in 

 that publication. Neither can I find that Deshayes has described 

 it elsewhere. Indeed the only ground for including it in the 

 Australian fauna rests upon the fact that four specimens in 

 Cuining's collection have a label "Adelaide " attached to them. 



Sowerby's figure 39 h is very incorrect. The shell is repre- 

 sented as acutely Leelcd at the base, the keel terminating at the 

 aperture, which appears flat beneath. Tliisis not the case in any 

 of the four shells in the Museum. The whorl also on the left- 

 hand side appears to slope very much, forming a somcAvhat acute 

 angle at the base. 



The last whorl in reality has a slight and not prominent carina 



