NEWTON : OPALIZED SHELLS OF NEW SOUTH AVALES. 227 



ornamentation of the species as exhibited in this specimen. The 

 sculpture is seen to consist of bold concentric depressed ridges and 

 broad shallow sulcations covered with fine concentric lineations, but 

 crossing them are numerous short, microscopical, vertical striatious, 

 as well as occasional longer and filamentous lines similarly directed, 

 mostly confined to the ventral region, such as may be seen on 

 the Viilves of both fossil and recent freshwater Pelecypoda, 

 being sometimes present in Corbicula cuneiformis of J. Sowerby, 

 from the older Eocene deposits of England and Europe, as 

 also in further fossil species of that genus ; it is besides seen 

 on Unioniform shells, for which examples of Unio tumidiis of 

 Ketzius in the Geological Department of the British Museum 

 (L. 10032) may be quoted, which were obtained from the Post- 

 riiocene deposits of the Lea jNIarshes near London ; and the character 

 is also apparent in Anodonta beckJesi, which I described some years 

 since before this Society (Proc. Malac. Soc, vol. ix, pp. 114-17, 

 pi. i, 1910) from the English Wealden formation. 



Dimensions. — Length 29, height 26 (approx.), diameter 15 mm. 



This species forms the type of Cyrenopsis, Etheriiige, jun., being 

 at first regarded as a doubtful Unicardium and afterwards as an 

 example of Mactra. A more complete study of the dentition enabled 

 the autlior to see its close connexion with Cyreniform shells like 

 Corbicula, from which it differed, however, in the possession of 

 a triangular, submedian, cardinal tooth in each valve, making two 

 instead of three teeth for both valves as in that genus. 



Locality. — Lightning Ridge, New South Wales. 



Collection. — British Museum (Geol. Dept., L. 21832). 



Distribution. — Lower Cretaceous of Queensland (Walsh Iliver) and 

 South Australia (Lake Eyre Basin). 



CriiENOPsis OPALLITES, Ethcridgc, jun. PI. VI, Figs. 11, 12. 

 ? Cyrena (?), n.sp., Giirich, Neues Jalirb., Beilage Band xiv, p. 486, 



pl. xix, figs. 5, 6, 1901. 

 Cyrenopsis opallites, Etheridge, jun. : Mem. Geol. Surv. New South 



Wales, Palifiontology, No. xi, p. 29, pl. v, figs. 12-17, 1902. 

 Description {original). — Shell ovate, moderately inflated ; cardinal 

 margins arched, ventral margins well rounded; anterior ends some- 

 what flattened, with rounded margins; posterior ends slightly 

 produced or nasute, the dorsal posterior margins straight and oblique, 

 the ventral rounded ; posterior slopes slightly flattened, narrow, and 

 generally inconspicuous ; umbones depressed, escutcheon long, deep, 

 and narrow ; ligament short. A.rticulus arched, longer on the posterior 

 than the anterior ; anterior cardinal of the left valve triangular, 

 projecting, and slightly obli(jue, posterior cardinal of the same valve 

 laminar; anterior lateral slightly curved, short, posterior lateral long, 

 distant, and straight. Central upper cardinal of the right valve 

 laminar and almost marginal, lower cardinal laminar and oblique ; 

 anterior lateral short and curved, posterior lateral long, distant, and 

 straight. Adductor impressions and pallial lines very faint. Sculpture 

 of concentric lamina?, with faint coincident lines. 



