139 



Surface with granular ribs. 



Elongate, suboval ; umbones subanterior. B. limatella. 



Id., posterior side attenuated. JB. consutilis. 



Trapezoidal, posteriorly keeled ; umbones anterior. 



B. simulans. 

 Ovate-oblong ; strongly ribbed on the posterior slope. 



B. pumila. 

 Maceodon. 

 Yalves closed ; umbones approximate ; posterior teetli lami- 

 nar horizontal ; anterior teeth few, short, oblique. 

 Sculpture of flat concentric ridges transversed by distant 

 riblets. M. Cainozoicus. 



Area pseudonavicularis, spec. nov. PI. xi., fig. 8. 



Shell elongate, subtrapeziform, tumid ; front margin 

 obliquely rounded ; posterior margin somewhat attenuated, ob- 

 liquely truncated, with the posterior slope strongly angulated;. 

 hinge line straight. Umbones anterior, distant, acute ; ventral 

 margin sinuately excavated ; inner margin of valves plain. 

 Surface ornamented with concentric fimbriated folds; posterior 

 slope unequally, radiately ribbed. In young specimens the sur- 

 face is unequally cancellated, and the radial ribbing on the 

 anterior and posterior areas is very pronounced. Hinge area 

 broad, with a well defined triangular area under the beak ; 

 teeth very numerous, small, transverse. 



Dimensions. — Greatest length, 27 ; width, 12"5 ; thickness- 

 through both valves, 14 millimetres. 



Localities. — Adelaide bore {R.T.) ; Table Cape {B. M. John- 

 ston !) . 



The living analogue of this species is A. navicidaris, Brug., 

 as known to me from Port Darwin, from which it differs in 

 the umbones being not near the front, in the somewhat emar- 

 ginate anterior side, and in the finer ribbing on the posterior 

 slope. 



Area equidens, spec. nov. PI. xi., fig. 9. 



Shell elongate-oblong, tumid, with a depression extending 

 from the umbo to the ventral margin, which is somewhat in- 

 sinuated ; anterior side acutely angular, posterior side elon- 

 gated, obtusely angular or truncated, with a roundly angular 

 posterior slope ; hinge line straight. Umbones at the anterior 

 third, narrow, acute, wide apart. Surface with concentric, 

 imbricating ridges and radial threads or ribs. The ornament 

 varies in respect to the relative strength of the radial ribs and 

 concentric ridges ; in some it is of the nature of fimbriated 

 concentric ridges, whilst in the other extreme it consists of 

 radial ribs variously thickened at the intersections with the 



