290 Annals of the South African Museum. 



ventral margin an acute but well-rounded angle, and with the hinge- 

 line an obtuse angle. Umbones large, incurved, pointed, with a 

 well-rounded carina extending to the postero-ventral extremity and 

 cutting off a steeply-sloping and flattened area which has a radial 

 furrow near its posterior third and a radial rib near its anterior third. 

 Hinge-line less than the greatest length of the valve. Hinge-area 

 broad, usually with from four to six ligament grooves. 



Ornamentation of the left valve consists of strong radial ribs 

 separated by flattened interspaces of greater breadth than the ribs. 

 Both ribs and interspaces are crossed by fine, fairly regular growth- 

 lines, and at distant intervals by a few growth-furrows. Near the 

 anterior end the ribs become rather smaller, and posteriorly they 

 may become rather closer together. In the interspaces there are 

 sometimes a few fine radial ribs. At a short distance in front of 

 the carina the ornamentation changes suddenly — the strong ribs 

 being replaced by much finer ribs separated by linear furrows. This 

 kind of ornamentation is continued on to the posterior area, but 

 becomes rather finer and may be indistinct on its posterior portion. 



On the right valve the radial ribs are broader than those on the 

 left, and are separated by narrow furrows ; the ribs may be absent 

 or indistinct near the anterior extremity, and continue with little or 

 no change to the carina. In well-preserved specimens the ribs bear 

 numerous transverse ridges. On the posterior area the ornamenta- 

 tion is much finer than on the rest of the valve. 



The lateral teeth are long and parallel or nearly parallel with the 

 hinge-margin, and bear rather irregular transverse ridges. There 

 are a few small, transverse median teeth. Margins of valves coarsely 

 crenulate. 



Length of hinge 27 . 25 . 24 . 14 mm. 

 Height of valve 28 . 27 . 26 . 13 „ 



Affinities. — This species resembles Area japetica Forbes,''' from 

 the Ariyalur, the Valudayur, and Trigonoarca Beds, but in the latter 

 the ventral margin has a greater curvature, the posterior extremity 

 is more rounded, the ribs on the left valve are more widely separated, 

 and the shell is relatively longer. 



The examples from Saghalien referred to Maerodon jaj^eticum (?) 

 by Schmidt f and those of Ciieidlcea saehalinensis of the same 



* Trans. Geol. Soc, ser. 2, vol. vii. (1846), p. 148, pi. xvi., fig. 2. Stoliczka, 

 Cret. Fauna S. India, vol. iii. (1871), p. 350, pi. xviii., figs. 6-11. 



t Petrefakt. Kreideformat. Insel. Sachalin. Mem. Acad. Imp. Sci. St. Petersb., 

 ser. 7, vol. xix., No. 3 (1873), p. 25, pi. v., fig. 5, pi. viii., fig. 8. 



