880 ZENATIOPSIS, 



Mactra howchiniana, Tate. 



1887. Mactra hoivchinkina, Tate, Trans. Roy. Soc. South Aust. vol. ix. p. 171, 



pi. xvii. figs. Za-b. 

 1893. Mactra howchiniana, Tate and Dennaut, id. vol. xvii. pt. 1, p. 225. 



Distinguislied from the preceding species in being elongately 

 ovate, and attenuate at the extremities ; surface finely concen- 

 trically ridged and striated ; pallial sinus large. 



Dimensions. — Height 21-5 mm. ; length 36"5 mm. 



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



L. 9880. Specimens of both valves. Purchased. 



Mactra hamiltonensis, Tate, 



1887. Mactra hamiltonensis, Tate, Trans. Roy. Soc. South Aust. vol. ix. 

 p. 171, pL xvii. figs. A.a-b, 



Shell shorter and broader than in M. axiniformis ; posterior 

 side straight; whilst the concentric striae are simple at the 

 sides instead of being exaggerated in thickness or obliquely 

 striated. The author remarks that it differs from the living 

 M. polita, Chemnitz, of South Australian seas, in having flatter 

 valves, in being less triangular in outline, proportionately larger, 

 and the ventral margin is not so broadly curved. 



Dimensions. — Height 15-5 mm. ; length 21 mm. 



Form, and Xoc.-^Miocene : Muddy Creek, Victoria. 



L. 9882. Examples of the neanic stage of growth. Purchased. 



Genus ZENATIOPSIS, Tate. 

 [Trans. Phil. Soc. Adelaide, 1879, p. 129.] 



"Shell equivalve, insequilateral, oblong; umbo anterior, supported 

 internally by a thick rib, extending, with a slightly backward in- 

 clination, half way across the valve ; narrowly gaping at both ends ; 

 cartilage-plate prominent ; cardinal teeth distinct, no lateral teeth ; 

 pallial sinus deep, horizontal." — Tate. 



The thick rib supporting the umbo internally is, perhaps, the 



