84 R. BULLEN NEWTON on 



being elevated, rounded, nodulated above, and bordered by a smooth, rounded 

 ray on each side ; costae divided by narrow interstices, and alternating at 

 margin with those of the other valve ; surface of valves furnished with close, 

 concentric, and fine striations ; margins thick, with tripartite serrations, and 

 pectinate within. 



DIMENSIONS. 



Adult. 

 Height ... ... ... ... ... ii millimetres. 



Length 15 



Diameter (closed valves) ... ... ... 8 



REMARKS. In a general way this shell is related to C. costcenodulosis, 

 although differing widely from that form in the possession of tripartite costae 

 and a small byssal aperture. The nodulose or central part of the ribs is 

 elevated and equidistantly separated from each other by a wide furrow, in the 

 floor of which runs a thin interstitial groove ; each side of the nodulated 

 section and on a lower plane, is furnished with a smooth, rounded rib. This 

 tripartite structure of the costae is quite well known among Eocene forms of 

 Cardita, such as C. carinata (J. Sowerby) 1 from British Lutetian deposits, 

 C. acuticosta (Lamarck) 2 from similar beds of Europe and Egypt, as also 

 C. viquesneli, 3 Archiac and Haime (which includes Cossmann's Venericardia 

 tripartite?) 4 from beds of the same age occurring in India and Egypt, all of 

 which species, however, differ from the present shell in contour being either 

 rhombic or rounded as distinct from a trigoniform outline, besides possessing 

 more slenderly constructed costae. Forms of Cardita bearing trigonoid 

 shapes and furnished as well with tripartite costae are of frequent occurrence 

 in the Egyptian Eocene, being represented particularly by C. mokattamensis 

 and C. fajumensis described by Oppenheim, 5 which have similarly wide 

 costae although more divided in structure and lacking generally the nodulose 

 ornamentation. This species is apparently of rare occurrence only six 

 specimens having been obtained. 



OCCURRENCE. Cutting No. 6. 

 COLLECTOR. Mr. Kitson. 



1 Mineral Conchology, 1820, Vol. 3, pi. 259, fig. 2, p. 106. 



a Ann. Mus. Hist. Nat. (Paris), 1806, Vol. 7, p. 57, ibid., 1807, Vol. 9, pi. 32, figs. 2. 



3 Desc. Anim. Foss. Nummulit. 1'Inde, 1854, part 2, pi. 21, fig. 7, p. 255. 



4 Bull. Inst. Egyptien, 1901, Ser. 4, No. I, p. 193. Separate copy with pi. 3, figs. 9, 10, 

 6 Palaeontographica, 1903, Vol. 30, part 3, pi. 8, figs. 7-11, 22-27, PP- i3> i5- 



