112 



The plica? only are usually continued as smooth angular ridges 

 on the umbonal portion, the whole surface of which is delicately 

 shagreen-sculptured. In some examples the shagreen-markings 

 cover the whole shell, whilst in others the plica' and raised 

 lines maintain their scaly ornament to the umbo. 



Pecten spondyloides, Tate. PI. iv., figs. 6 and 7. 



'Reference. — Proc. Eoy. Soc, S. Australia, vol. iv., p. 44?, 1882. 



Shell equivalve, equilateral, about as long as high, inflated,, 

 covered with numerous spiniferous ribs. There are usually 

 seven or nine primary ribs, two or three secondaries, and a 

 variable number of tertiaries between each pair of primary 

 ribs, all similarly ornamented. Front margin of valves- 

 curved, slightly crenulated, not at all angular. Ears equal, of 

 moderate size, triangular, outer margin perpendicular ; there 

 is no byssal sinus. 



Yarieiy. — PL lY., fig. 7. With the prickly scales of the in- 

 terstitial ribs reduced to spine-like serratures, and the spines 

 on the primary ribs slender and distant ; regular concentric 

 strise mark the whole surface. 



Dimensions of the figured specimen. — Length and height,. 

 44 ; thickness through both valves, 34 millimetres. A large 

 perfect specimen measures 90 mills, in diameter, whilst frag- 

 ments indicate a greater magnitude. 



Localities. — Oyster banks of the Upper Aldinga series at 

 Aldinga Bay, Hallett's Cove, and Adelaide. The variety in 

 the raggy limestones at Mannum. 



This very handsome shell has much the appearance of a 

 Spondylus, hence its trivial name, and more particularly of 

 8. imperialis, of the Chinese Seas ; however, it is a Pecten, 

 having an edentulous hinge ; moreover, the regular curved 

 umbos of both valves presented by shells of all ages are cha- 

 racters not belonging to Spondyhts. 



Pecten Gambierensis, Tenison- Woods. 



Beference. — Proc. Phil. Soc, Adelaide, 1865, pi. i., fig. 2. 



Shell thick, inequivalve, the left valve regularly convex, the 

 right flatter ; inequilateral by projection of the anterior area, 

 ornamented with from five to seven radial folds, which together 

 with the interspaces are covered with imbricating, granular^ 

 close-set ribs, the sulci between the ribs regularly transversely 

 striated. Ears unequal, the anterior one small, truncated ; 

 the posterior larger, rounded, and strongly ribbed. 



Dimensions. — Length and height, about 30 millimetres. 



Localities. — Coralline limestone at Mount Gambler and 

 Mosquito Plains {T. Woods, B.T.). 



The ornament varies in the closeness and stoutness of the 

 radial ribs and their granulations, whilst the plica? are some 



