99 



'Cliffs, Great Australian Bight, Soiitli Australia (i2. Tate), 

 Chatham Islands, New Zealand {Hutton). 



Ohservations. — Our fossil cannot be mistaken for the recent 

 G. angulata, Lamarck, but it bears a close resemblance to the 

 'Cretaceous Gr. vesicidaris, Lamarck, from which it differs in its 

 more triangular outline, larger lobation, and in the superior 

 Talve being lamellose. In my description of the chalk-rock of 

 the cliffs of the Grreat Australian Bight I have remarked that, 

 *' on a cursory inspection one is struck by its similarity to the 

 chalk of England, heightened by the presence of layers of 

 black flints and of fossils with a Cretaceous facies such as 

 jSalenia {S. tertiaria, Tate), Cidarls (C. and red a sice ^ Duncan), 

 Gryphcea (G. tardei, Hutton), like G. vesicidaris, a Terehratula 

 {T. suhcarnea, Tate) barely distinguishable from T. carnea^ 

 Terehratidina, &c." Trans. Eoy. Soc, S. Aust., 1879. 



Hitherto G. tardahsi^ been found at the Australian localities 

 only in the lowest beds of the marine series of the Older Ter- 

 tiary. I am not sure if our fossil is correctly named, as I have 

 not had specimens of the New Zealand species for comparison, 

 it answers fairly well to Hutton's diagnosis, except that it is 

 only of about half the size. The original description reads as 

 follows : — Irregularly ovate, umbo of left valve incurved and 

 bent slightly forwards ; exterior smooth, with concentric stria? ; 

 right valre rather concave, often thickened near the margin, 

 much smaller than the left valve ; area broad triangular, dis- 

 tinctly transversely striated ; muscular impression suborbicular, 

 rather flattened above where it is deeply sunken, posterior, 

 placed high up ; height 2'4, length I'T inches. 



Gejjus Dimya, Bouaidt. 

 The genus Dimya was founded for an oyster-like fossil of 

 the Parisian Eocene with a second adductor impression, and 

 by most conchological writers has been placed in the family 

 Ostreidae, the additional scar being regarded as the homologue 

 of the small anterior scar in Pecten. Tyron* seems to have 

 studied a living example of the genus dredged off the Antilles, 

 w^hich he describes as "essentially an oyster having two adductor 

 muscles, the exterior layer of the shell pearly, the inner por- 

 cellanous, hinge with a pit like Hinnitesy He follows Stolickza 

 (in "Cretaceous Pelecypoda of Southern India") in placing the 

 genus in the sub-family Yulsellina^, family Acicididw. As the 

 anatomy of Dimya agrees with tliat of Ostrea, the original 

 position assigned to the genus in the scheme of classificatioii 

 would thus appear to be the correct one, despite the fact of its 

 dimyarian character. 



* Systematic Conchology, vol. iii., p. 281, 1881. 



