100 



The two new species which I refer to Dimya have the general' 

 aspect of JPlicatula rather than of Ostrea ; whilst the two 

 diverging cardinal ridges make an approach to Placuna, though 

 functionally different. The internal characters presented by 

 them are as follows : — ■ 



Eight valve attached, with two diverging cardinal ridges 

 crenulated for the greater portion of their length ; cartilage 

 pit triangular, with a raised margin, within the angle formed 

 by the cardinal ridges. Posterior muscular impression large, 

 oval, in about the same position as the single scar in PUcatuJa ; 

 the anterior scar is ovate, small but deeply impressed, close 

 under the end of the cardinal ridge; pallial line entire. Left 

 valve free, with two diverging cardinal furrows crenulated 

 within the grooves. 



SYJs'OPSIS OF SPECIES. 



Coarsely radially ribbed; internally ribbed. D. sigiUafa . 

 i'inely radially ribbed ; margin only ribbed. D. dissimiJis. 



Dimya dissimilis, spec. nov. PI. iii., figs. 9a — 9c. 



Shell ovate-oblong to ovate-triangular ; inequivalve, inequi- 

 lateral, posteriorly oblique ; umbo sub-central, dorsal line 

 usually straight. Eight valve attached by varying extent of 

 surface ; free part obliquely elevated, slightly convex, orna- 

 mented by many high-rounded ribs frequently bifurcating 

 towards the front, crossed by lamellcT which give rise to im- 

 bricating scales or spinous scales on the radial ribs. Left 

 valve free, flattish, a little swollen in the umbonal region, de- 

 pressed centrally, and elevated at the margin ; scaly fringed 

 with imbricating lamellae. Interior of both valves with radial 

 riblets interposed between the pallial line and the shell margin, 

 most conspicuous in the dorsal region. 



Dimeiisions. — Lt-ngth, 10 ; height, 13 millimetres. 



Localities. — South Australia : Gastropod-bed, near Morgan, 

 and elsewhere in the Middle Murraviau, in the raggy lime- 

 stones at Mannmn, on the Eiver Murray ; Salem, near Calling- 

 ton, on the E. Bremer : Eolls Point, Nepean Bay, Kangaroo 

 Island. Victoria : Muddv Creek, Hamilton, and Corio Bav, 

 Geelong {B.T.) 



Dimya sigillata, spec. nov. Plate viii., figs. Sa — 86. 



Shell ovate-oblong, inequivalve, subinequilateral, posteriorly 

 somewhat oblique ; umbos subcentral, dorsal line usually 

 straight. 



Eight valve attached by a large surface, free part much ele- 

 vated, ornamented by numerous rounded radial riblets and a 

 few imbricating lamelhT of growth. Left valve free, slightly 

 concave, except in the umbonal region, included within the 



