109 



This species is more depressed, equilateral, and lias more 

 ribs than P. antiaustralis and P. australis, whilst the anterior 

 ear of the left valve is not winged. 



This species is dedicated to the memory of M. Peron, the 

 naturalist to the Baudin Expedition, as a mark of my apprecia- 

 tion of his geological observations on Kangaroo Island. 



Itemarks on the affinities of the three foregoing species : — ■ 



They agree in one particular, which distinguishes them from 

 P. australis and P. antiaustralis, namely, that the anterior ear 

 of the left valve is not winged. 



The oldest species in time is P. Flindersi, which is depressed, 

 and ornamented with numerous, narrow, rounded ribs, smooth 

 or distantly scaly ; in P. Eyrei the ribs are fewer in number^ 

 broad, and densely scaly ; whilst P. Peroni, which occupies an 

 intermediate geological position, has the numerous narrow,, 

 but acute ribs of the former, and the dense scaly ornament 

 of the latter, diverging, however to the spinous scales of 

 P. australis. 



Pecten Sturtianus, si^ec. nov. Plate vii., figs. 2a — 2c. 



Shell nearly orbicular, convex, equivalve, equilateral ; about 

 30 flatly rounded radial ribs covered with distant, thick, imbri- 

 cating scales, the alternating furrows about as broad as the 

 ribs, marked with transverse or oblique lines. Margin of 

 valves crenulate-undulate. Eight valve with unequal ears ; 

 the posterior larger, triangular, and subaliiform, strongly rayed 

 and granular or spinosely scaly ; the anterior ear triangular, 

 faintly three-rayed, with perpendicular lamellae conspicuous 

 only towards dorsal margins, and obliquely striated. Left 

 valve, posterior ear elongately produced, narrow, deeply exca- 

 vated by a byssal sinus, four nodular- scaly ribs ; anterior 

 small, similarly ornamented to corresponding ear in the right 

 valve. 



Dimensions. — Length, 18 ; height, 18"5 ; and thickness 

 through both valves, 10 millimetres. 



Localities. — ISTot uncommon in the Calciferous sandstones of 

 the E. Murray cliffs at Blanchetown, &c. ; raggy limestones at 

 Mannum (P. T.) ; rare Muddy Creek, Hamilton. 



The species is dedicated to the memory of Captain Sturt, the 

 pioneer geologist of the basin of the Lower Murray river. 



P. Sturtianus has a general resemblance to P. Malvince, of 

 the Viennese Miocene. 



Pecten Aldingensis, spec. nov. PI. vii., figs, la — Ic. 

 Shell orbicular, or a little longer than high, thin, sub- 

 equilateral, inequilateral. Eight valve moderately convex, 

 left valve flatter, ears unequal ; both valves ornamented with 



