PERMO-CAKBONIFEROUS PELECYPODA — ETHERIDGE. 18 i 



particularly in the case of the last with its deeply emarginate 

 posterior wing. 



Log. and Horizon. — Mouth of Crooked River, near Gerringong, 

 Illawarra District — Upper Marine Series. 



Genus Mytilops, J. Hall. 



(1st Report State Geol. N. York, 1884, p. 15.)* 



Mytilops 1 ravensfieldensis, sp. nov. 



(PI. xxxiii., figs. 6 - 7). 



Sp.Char. — Shell (left valve) narrow, somewhat elliptical, oblique, 

 generally raytiliform, gibbous and transversely arched posterior to 

 the umbone ; hinge line faintly arched in the cast, but less than 

 the length of the shell ; no ligaiiiental furrows, but beneath the 

 umbo is a single oblique cardinal fold, posterior teeth or folds none; 

 ventral margin very obliquely inclined ; umbone terminal, no 

 anterior end ; posterior end, or general body of the shell convex 

 immediately behind the umbone, graduilly flattening towards the 

 rounded posterior margin, where the valve is broad ; anterior 

 muscular impression, invisible and the posterior very faint and 

 high; pallial impression well marked and continuous, the exterio- 

 pallial margin wide; sculpture unknown, but probably concentric 

 and non-radiate. 



Obs. — Allied either to Mytilops or Mytilarca. It possesses 

 the outline of the latter genus, and approaches the former in its 

 simpler hinge structure ; difters from Mytilarca in the absence 

 of a ligamental area and posterior teeth, and from Mytilops in 

 the presence of the cardinal fold. So far as our Permo-Carboni- 

 ferous fauna is concerned this is again an undescribed form. 



Log. and Horizon. — Raveusheld Quarry, near Farley — Lower 

 Marine Series. 



See note to precedingjpage. 



