25-4: CRETACEOUS LAMELLIBRANCHIA. 
the figures given by several authors, that species varies considerably, so that it 
seems probable that when more Hnglish specimens have been obtained it will be 
possible to refer them definitely to M. semicostata. 
Distribution.—Lower Greensand of Furze Hill, Faringdon. 
Genus—Goniomya, L. Agassiz, 1842. 
(‘ Etudes crit. Moll. Foss.,’ Myes, pp. xii, 1.) 
GoniomyA ArcutAct (Pictet and Renevier), 1855. Plate XLII, figs. 4, 5. 
1855-6. TuHracita Arcuraci, F. J. Pictet and E. Renevier. Foss. Terr. Aptien 
(Matér. Pal. Suisse, ser. 1), p. 67, 
pl. vu, fig. 5. 
1858. -- — Pictet and Renevier. Ibid., p. 176. 
1865. PHo~apomya tTHRACIoIDES, F’. J. Pictet and G. Campiche. Terr. Crét. Ste. 
Croix (Mater. Pal. Suisse, ser. 
4), p. 92 (Goniomya). 
1870. Gontomya Arcuiact, F. Stoliczka. Paleeont. Indica, Cret. Fauna 8. India, 
vol. iu, p. 75. 
Description.—Shell oblong, convex, nearly equilateral. Anterior margin 
rounded. Ventral margin shghtly convex or nearly straight, nearly parallel with 
the dorsal margin. Posterior margin truncated, oblique, shghtly convex, forming 
a rounded angle with the ventral margin and an obtuse angle with the postero- 
dorsal margin. Umbones of moderate size, with a faint rounded carina extending 
postero-ventrally, above which the shell is compressed; lunule and escutcheon 
elongate, depressed, limited by carine. 
Ornamentation: Anteriorly to the umbones there is a ribbed area in which the 
ribs extend obliquely backwards ; posteriorly to the umbones is another ribbed area 
in which the ribs are nearly perpendicular to the postero-dorsal margin, but 
shghtly curved ventrally. The anterior, ventral, and postero-dorsal parts of the 
shell are without ribs, and show growth-lines only. Near the umbo the ribs of 
the two areas are connected by horizontal ribs, but ventrally these horizontal ribs 
are absent or indistinct. Some parts of the shell are marked by rows of small 
pits. 
Measurements : 
(1) (2) (3) 
Length :; 33 : 28 : 19 mma. 
Height : 19 16 a 
99 
(1—3) Crackers, Atherfield. 
