115 



P. lunularis, Horn., o£ the Lias. It is highly probable that 

 Tenison- Woods confounded this species with P. ])leuronectes in 

 bis record of the occurrence of the recent species in the ]Mount 

 G-ambier limestone, as the only smooth pecten known to me to 

 be found there is P. SocJistetteri. 



Pecten lucens, spec. nov. 



Shell nearly orbicular, slightly mequivalve, equilateral, a 

 little gaping at each side below the ears, compressed, thin, 

 pellucid, externally smooth but radially and concentrically 

 striated under the lense ; internally rayed with from 30 to 36 

 pairs of ribs. Eight valve slightly convex from the umbo to 

 the anterior margin ; ears equal, straight, truncated, trans- 

 versely striated and faintly radially ridged. Left valve de- 

 pressed in the umbonal region ; ears obliquely truncated, 

 transversely striated, upper margin sometimes dentate ; hinge 

 area internally thickened, bearing at each anterior corner a 

 subacute boss. 



Dimensions. — Transverse and longitudinal diameters 48 

 millimetres ; thickness through both valves 10 millimetres. My 

 largest specimen measures 100 millimetres in the diameters. 



Localities. — Oyster bed, Aldinga Bay ; calciferous sandstone 

 of the Eiver Murray Cliffs at Blanchetown. 



P. lucens differs from all living species of the group by the 

 greater number of the internal radial ridges, and by the same 

 character it is separable from the Chilian fossil species, 

 P. Darwinianus, D'Orb., to which it bears a close resemblance. 



Pecten Zitteli, Hutton. PI. vii., figs. 3a— 3c. 



'Reference. — Catalogue Tertiary Mollusca of IS'ew Zealand, 

 p. 32, Xo. 118 (1873). 



Synonym. — Pecten sp., Zitfel in Pal^eoutologie von jSTeu- 

 Seeiand, p. 53, t. 9, figs. 16 and 3, 1864 



Amusium Atkinsoni, B. M. Johnston, in Proc. Eoy. Soc, 

 Tasmania, 1880, p. 41. 



Shell small, sub-orbicular, compressed, equilateral, equivalve. 

 Interior of both valves concave, shining, with nine or eleven 

 ribs which terminate truncatedly near the margin. Eight 

 valve reticulatedly striated or ridged ; left valve concentrically 

 striated ; ears unequal. The exterior ornament of the right 

 valve varies very much in respect of the number and thickness 

 of the radial and concentric threads ; usually the radial threads 

 are stouter than the raised concentric lines, but this form 

 merges on the one hand into a fenestrated ornament, and on 

 the other to one in which the radial ridges are very prominent 

 and minutely scaly. Ears of right valve unequal, the posterior 

 larger and triangular, cancellate ; anterior triangular, with, 

 concentric scaly lamella). 



