110 



about 50 narrow, rounded, sub-depressed ribs, straight or 

 ■slightly ilexuous, with narrower interspaces, which are sculp- 

 tured with oblique linear sulci and punctures ; towards the 

 front margin a few indistinct concentric lamellae cross the 

 ribs. 



Right valve with the ears very unequal, the anterior aliiform, 

 radially and concentrically scaly-striated, ventral margin 

 sinuated for the passage of a bj^ssus ; posterior ear triangular, 

 vertically and radially scaly-striated. 



Left valve with unequal ears, the posterior one the smaller ; 

 both triangular, and radially costated and scaly. 



Dimensions. — Length and height, 32 millimetres. 



Locality. — Grlauconitic limestone, Aldinga Bay. 



Pecten Yahlensis, Tenison- Woods. 



References.— Vh\\. Soc, Adelaide, 1865, t. 1, fig. 4 ; P. Yah- 

 lensis, var. semildBvis, McCoy, Prodr. Pal. of Victoria, Decade 

 iv., t. 34. 



Shell sub-orbicuiar, thin, equilateral ; valves unequal, and 

 with dissimilar sculpture. 



Right valve deeper than the left, moderately convex, polished ; 

 surface radiated with numerous (60-70) sub-equal, nearly 

 straight, narrow, flatly-rounded ridges, separated by shallow 

 concavities, rather less than the width of the ridges, crossed 

 by distant concentric lines of growth. Ears, with the posterior 

 one a little larger than the anterior ; both slightly obtuse- 

 angled, radially ridged, and marked with concentric lines of 

 growth, which rise on the dorsal margin as projecting angular 

 scales ; anterior ear slightly sinuated anteriorly for passage of 

 byssus. 



Left valve nearly flat, surface radiated with nearly straight, 

 narrow, rounded ridges, about one-third of their width apart, 

 •crossed by sharp, erect, crowded, concentric lamellcT. Ears 

 about equal, slightly obtuse-angled, radially ridged, crossed by 

 concentric lamellse, which form a serrated fringe on the dorsal 

 margin. 



In the var. sulJcevis the right valve is quite smooth, whilst 

 •another variety has the rostral portion smooth, and the mar- 

 ginal portion radiately ridged. 



Dimensions of average sized specimens. — Length and height, 

 about 55 millimetres ; but specimens are known from four to 

 five inches in diameter. 



Localities. — South Australia: Mount Gambier limestone 

 {Tcnison-Woods) ; raggy limestones at Mannum, R. Murray 

 .{B.T.) 



Victoria: Muddy Creek {R.T.); Mordialloc ; Corio Bay; 

 Bairnsdale ; Schnapper Point, Hobson's Bay ; near mouth of 

 Sberbrook River {JLcCoi/). 



