68 R. BULLEN NEWTON on 



Family ARCID^. 



Fossularca afrioana, sp. nov. 



PLATE 8, figs. 14-17. 



DESCRIPTION. Shell strong, small, subrhomboidal, trigoniform, ventricose, 

 slightly inaequivalve, inaequilateral, length nearly i J times the altitude ; 

 anterior margin rounded, posterior region slightly excavated, abruptly trun- 

 cated, deep, ventral border straight and produced to meet the posterior 

 angle ; ligament furrow short, narrow and tapering in front, widest and 

 sagittate behind (i.e., with closed valves), not chevroned, perpendicularly 

 striated, succeeded by smooth terminations ; without triangular fossette 

 beneath the beaks ; umbones anterior, incurved, moderately remote ; sculpture 

 unequal, composed of innumerable, elevated, rounded, radial costae of irregular 

 strength crossed by microscopically fine, close, concentric lines, radial costae 

 of left valve fewer being more distant and thicker anteriorly than those of 

 the opposing valve ; hinge line straight, short, slightly arched within, bearing 

 about 40 closely arranged, continuous denticles, the central and smallest being 

 vertical, the terminal divergent ; inner margins crenulate. 



DIMENSIONS. 



Young. Adult. 



Height 5 ... 12 millimetres. 



Length ... ... 7^ ... 17 



Diameter (closed valves) ,.. ... 4 ... 14 



REMARKS. The species here described approaches in general characters 

 Area lactea, Linnaeus, from the Atlantic, which represents the type of 

 Cossmann's Galactella j 1 it differs, however, in its more ventricose umbonal 

 region, in its stronger and more abrupt carination, the wider and more 

 acuminate postero-ventral end, its unequal valves, pairs of which show a 

 difference in their individual ornamentation, the left being rather longer than 

 the right and possessing slightly fewer radial costae. Some small European 

 Arciform shells of Eocene age have been referred by Cossmann to his genus 

 Foss^llarca ) z the type of which is Area qiiadrilatera of Deshayes, from the 

 Lutetian beds of the Paris Basin, which is characterised by the presence of 



1 Act. Soc. Linn. Bordeaux, 1912, Vol. 66, p. 312. 



2 Ann. Soc. R. Mai. Belgique, 1887, Vol. 22, p. 138. 



