136 



face ornamented with broadisli depressed transverse and 

 narrow radial ribs. TJmbones minute, subterminal, obtuse ; 

 no area ; hinge-line thick, obtusangular ; ligamental pit exca- 

 vated in the hinge-line, oblique, lanceolate, directed backwards ; 

 anterior to the pit are three suberect denticles, and posteriorly 

 four longitudinal teeth. Internal margin of valves crenulated, 

 more prominently so in the posterior part. 



Dimeiisions. — Length from umbo to post-ventral margin, 

 5"5 ; width, 5 "5 ; thickness through both valves, about 4 milli- 

 metres. 



Localities. — Turritella-beds, Blanche Point, Aldinga Bay, 

 and glauconitic argillaceous sands, Adelaide bore. 



This species has a general resemblance to L. iniquidens, 

 Sandb., but wants the auriculated antero-dorsal margin, and 

 has fewer hinge teeth. 



G-EIfUS PECTUIfCULrS. 

 STIfOPSIS OF SPECIES. 



I. Finely radially striated. 



Orbicular, slightly oblique. P. Cainozoicus. 



II. Radially ribbed. 



Eibs, about 39 ; wider than long. P. laticostatus. 



Eibs, about 29 ; longer than wide. P. IlcCoyii. 



Hibs, about 29 ; subtrigonal. P. suhtrigonalis. 



Eibs, about 24, elevated ; orbicular, tumid. P. convexus. 

 Eibs, 40 or more ; orbicular, depressed. P. lenticularis. 



Pectunculus Cainozoicus, T. Woods, sp. Plate x., figs. 8a— 8b. 



Reference. — CucullcBa Cainozoica^ T. Woods, Proc. Roy. Soc, 

 Tasmania, for 1876 ; p. 111. 



" Shell roundly trigonal, oblique, globose, smooth, faintly 

 and closely marked with radiating ribs and concentric striae, 

 the latter well defined and somewhat rugose at the margin and 

 sides. TJmbones very acute and recurved. Ligamental area 

 arched, broad, with six straight grooves on each, which are 

 well defined, and overlap each other alternately under the 

 umbo ; hinge-teeth, 6-7, bent under the hinge, and then bicus- 

 pidate. Margin of valves finely pectinated with very distinct 

 crenulations, which continue in young shells all round as far 

 as the hinge. Young shells are also more quadrate, and have 

 the angular ears slightly developed" (T. Woods). 



Var., pi. X., figs. 8a — 8^. — This differs from the type in being 

 more orbicular, less narrowed at the hinge-line — characters 

 very conspicuous in young shells. The variety is hardly separ- 

 able from F. pulvinatus, Lamk., of the Parisian Eocene, which 

 is, however, more gibbous at the umbones, and is equilateral. 



