PLACUNANOMIA. 303 



sub-orbicular, rather flattened above, where it is deeply sunken, 

 posterior placed high up." 



It is not without some hesitation that the specimens in the 

 Museum are assigned to this genus, their state of preservation 

 being such that many of the essential characters cannot be satis- 

 factorily made out. In the absence of more perfect material these 

 South Australian fossils may, however, be provisionally identified 

 with G. tarda. 



Dimensions (as given by Professor Tate, op. cit.). — " Inferior 

 valve, height 45 mm. ; breadth 32 mm. ; thickness 23 mm." 



Form, and Loc. — Tertiary : liullarbor Plains, South Australia. 

 L. 10524. Several imperfect examples of the left valve. 



H. Y. L. Brown Coll. 

 L. 10526. Left valve of the adult. H. Y. L. Brown Coll. 



Family ANOMIID.^. 

 Genus PLACUNANOMIA, Broderip. 



[Proc. Zool. Soc. 1832, p. 28.] 



One valve carries two tangential muscular impressions towards 

 the centre, the upper one appertaining to the muscle of the byssus, 

 the lower to the adductor of the valves ; opposing valve perforated. 



Type. — Placunanomia cumingii, Broderip. 



Placunanomia ione, Gray. 



1849. riacunanomia ioiie, Gray, Proc. Zool. Soc. p. 12.3. 

 1873. Placunanomia imie, Ilutton, Cat. Marine Moll. N.Z. p. 84. 

 1880. Placunanomia ionr, Ilutton, Man. N.Z. Moll. p. 174. 

 1886. Placunanomia ione, Tate, Trans. Roy. Soc. South Aust. vol. viii. 

 p. 101, pi. V. figs. la-b. 



Shell orbicular, irregular, slightly convex, or rarely very convex, 

 horny-pellucid. The specimens in the Museum collection are not 

 well preserved, but Professor Tate remarks that the surface of the 

 unattached valve is "ornamented with imbricating scaly lamellne 

 and radial threads or ridges ; umbo sub-marginal, depressed, with 

 a slight back curvature. Ligamontal scar within the umbonal 

 cavity transverse, oblong, circumscribed by a raised border, radially 



