298 



It is impossible to recognize this species from the caricature 

 given on the plate above referred to ; but Professor Tate describes 

 it so nainutely that the figure may almost be dispensed with. He 

 remarks that the shell is "long, narrow, slightly bent; slightly 

 swollen at a little nearer the anterior than the posterior end, more 

 conspicuously so on the convex curve, which is a little nearer to 

 the posterior end than is the bulging on the concave curve. 

 Anterior to the inflation the tube is slightly laterally compressed. 

 The mouth is slightly oblique, oval, with a thin and sharp edge ; 

 the posterior opening is round, thickened within, and bevelled to 

 a sharp edge, inconspicuously mucronately produced on the convex 

 side, corresponding with a faint internal rib, and slightly insinuated 

 laterally. Surface smooth, polished, microscopically concentrically 

 striated, and with faint indications of opaque transverse bands." 



Dimensions. — Length 7 mm.; width of median inflation r75mm. 



Form, and Loc. — Eocene : Muddy Creek, Victoria. 



G. 9390. Several examples of the adult. Furchased. 



Class LAMELLIEEANCHIATA. 

 Order TETRABRANCHIA. 



Family OSTREID^, 

 Genus OSTE,EA, Linnseus. 



[Syst. Nat. ed. 10, 175S, p. G96.] 



Shell irregular in shape, attached by the left valve, which 

 is the larger and the more convex ; right valve usually flat 

 or concave, often smooth, and minus the radiating ridges which 

 are usually so conspicuous on the other valve ; lines or corrugations 

 of growth prominent on both valves ; ligamental area triangular or 

 elongate, symmetrical; structure laminated, subnacreous; muscle- 

 scars large, well pronounced, subcentral. 



Type. — Ostrea edulis, Linnseus. 



