11 



This is a very distinct form, and is easily recognised by the 

 regularly, alternating large and small riblets. 



Family Pectenidje. Genus Steeblopteeia. (McCoy.) 

 Shell ovate or rounded, obliquely extended towards the 

 anterior side ; posterior wing broad, undefined, nearly rec- 

 tangular, extending nearly as far as the posterior margin of the 

 shell ; anterior ear small, deeply defined ; surface smooth or 

 radiatingly ridged ; one large, faintly-marked muscular impres- 

 sion a little behind the middle ; one short, narrow tooth slightly 

 diverging from the hinge line on the posterior side of the 

 beaks ; ligament confined to a narrow, simple facet on the 

 hinge margin. 



These shells differ from the short- winged Avicute to which 

 they are most allied by the obliquity of the body of the shell 

 towards the anterior instead of the posterior side. Carboni- 

 ferous. (Tryon.) 



Steeblopteeia Moetonii. (nov. sp.) 

 Shell small, somewhat ovate, longer than broad, obliquely 

 extended towards anterior side ; hinge line straight ; beak 

 small, acute, situated near posterior shoulder ; posterior wing 

 reduced to a lineal sunken border extending along the whole of 

 the posterior side ; anterior ear small, rectangular ; posterior 

 side, well-defined, short, oblique, straight, nearly as long as 

 hinge line ; anterior side rounded towards inferior angle ; 

 anterior ridge well-defined, obtusely rounded near umbo, con- 

 tinues well-defined, near and parallel to anterior slope ; surface 

 smooth, with a few distant, faintly-defined, concentric lines _ of 

 growth which are more pronounced towards ventral margin ; 

 ventral margin rounded at anterior side, thence gently curving 

 towards posterior slope, 



Length, 24 millimetres ; height, 22 mil; length of hinge 

 line, 12 mil. 



Casts common in Upper Palaeozoic marine beds, One Tree 

 Point and Porter's Hill, near Hobart. 



Family ANATiwiDiE. Genus Caediomoepha. (Koninck.) 

 Shell isocardia-shaped, smooth or concentrically furrowed ; 



umbones prominent, hinge edentulous ; hinge margin with a 



narrow ligamental furrow, and an obscure internal cartillage 



groove. (Tryon.) 



Caediomoepha geyphoides. (de Koninck.) 

 Shell globular, inflated; umboes remarkably arched and 



laxly recurved ; approximating surface of valves ornamented 



with fine, regular, concentric lines of growth. 

 _ Length, 75 millimetres ; thickness across valves (somewhat 



distorted and compressed), G7 mil. 



