378 MESODESMA. 



differs also in other particulars. It is sculptured externally with 

 concentric linear incisions, which become roughened on the 

 angulate posterior area. 



Dimensions. — Height 15 mm. ; length 30-5 mm. 



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



L. 4818. Specimens of both valves. 



Presented by John Dennant, Esq^. 



L. 9890. Examples of the neanic and ephebic stages of growth. 



Fur chased. 



Gari sequalis, Tate (sp.). 



1885. Psammobia cequalis, Tate, Southern Science Record, January, p. 4. 

 1887. Psammobia cequalis, Tate, Trans. Eoy. Soc. South Aust. vol. is. 



p. 168, pi. xvi. fig. 10. 

 1893. Psammobia (equalis, Tate and Dennant, id. vol. svii. pt. 1, p. 225. 



The absence of a posterior keel serves to readily distinguish this 

 species from G. hamiltonensis ; surface with closely -set raised con- 

 centric lineations. 



Fimensions. — Height 14'5 mm. ; length 28 mm. 



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



L. 4819. Right valve, of the neanic stage of growth. 



Presented hy John Dennant, Fsq. 



L. 9891. Series illustrating stages of growth. Purchased. 



Eamily MESODESMATID^. 



Genus MESODESMA, Leshayes. 

 [Ency. Metli. Vers. t. ii. 1831, p. 441.] 



Shell subtrigonal, depressed ; anterior side the longer ; hinge 

 thick, carrying a spoon-shaped depression for the ligament, in the 

 centre, a small bifid or double cardinal tooth in front of the ligament 

 pit ; anterior and posterior lateral teeth double on the right valve, 

 single on the left ; pallial sinus more or less deep. 



Type. — Mactra donacia, Lamarck. 



