138 



Pectunculus convexus, spec. nov. Plate xi., figs. 7a — 76. 



Sbell solid, orbicular, but slightly transverse, tumid ; sub- 

 equilateral ; umbones approximate, radiately ribbed. E/ib» 

 about 24, rounded, elevated, interspaces concave wider than 

 the ribs, crossed all over with thick concentric wavy laminae 

 becoming finer towards the front. Inner margin of valves 

 strongly crenate. Cardinal teeth about ten on each side. 



Dimensions. — Length, 31 ; width, 33 ; thickness through both 

 valves, 22 millimetres. 



Localities. — Muddy Creek. Imperfect specimens oyster 

 banks North-west Bend on the E. Murray ; Hallett's Cove and 

 Aldinga Bay. 



This species has some resemblance to the recent P.Jlahellatus, 

 T. Woods, but is more inflated and with wider interspaces be- 

 tween the ribs. 



Pectunculus lenticularis, spec. nov. Plate xi., fig. 1. 



Shell rather thin, orbicular, but slightly transverse, de- 

 pressed, equilateral ; radiately ribbed. Kibs numerous (more 

 than 40), very fine, rounded, narrower than, or about as wide 

 as, the interspaces, crossed all over with fine concentric wavy 

 lines. Inner margin of valves narrowly toothed ; umbones very 

 small, approximate ; ligamental area very small, cardinal teeth 

 11 on each side. 



Dimensions. — Length, 31 ; width, 29 ; greatest thickness 

 through both valves, at about one-third the distance from the 

 front, 12 millimetres. 



Locality. — Glauconitic sands, Adelaide bore. 



SUB-FAMILY AECINJS. 

 Synopsis of Species. 

 Aeca. 

 Valves gaping ventrally ; umbones high, wide apart. 



Hinge teeth numerous, transverse. A. pseudonavicularis. 

 Hinge teeth few, all oblique. A. equidens. 



Bakbatia. 

 Yalves closed or sinuated ventrally ; umbones approximate ; 

 teeth numerous, transverse, gradually becoming larger 

 and more oblique towards the extremities. 

 Transversely oblong ; left valve radially ribbed ; right 

 valve smooth, with contused impressions. 



D. dissi^nilis. 

 Oblong with concentric ridges thickly granulose or pli- 

 cate ; gibbous. B. crustata. 

 Elongate-oblong, with concentric fimbriated ridges. 



D. celleporacea. 



