38 CRETACEOUS LAMELLIBRANCHIA. 



On account of the name ornata having been previously used by d'Orbigny and 

 by Buvignier for other species it is necessary to substitute some other name. 



Types. From the Cambridge Greensand (indigenous), preserved in the Sedgwick 

 Museum, Cambridge. 



Distribution. Cambridge Greensand (indigenous). Lower Chalk of Burwell. 



LIMA (MANTELLUM) BRITANNTCA, sp. nov. Plate VI, figs. 13 a d. 



1857. LIMA ELEQANS, J. W. Salter. Quart. Journ. Geol. Soc., vol. xiii, p. 85, pi. ii, 



fig. 3 (non elegans, Nilsson). 



Description. Shell moderately convex, sub-quadrate or nearly oblong, very 

 oblique. An tero -dorsal and postero- ventral margins more or less parallel ; pos- 

 terior margin rounded. Ears of moderate size, with a few ribs on the inner 

 portions, and with distinct growth-lines; the anterior larger than the posterior 

 ear. Anterior area not distinctly limited, covered with ribs similar to those on the 

 rest of the valve but of nearly uniform size. 



Ornamentation consists of eighteen main ribs, which are strong on the anterior 

 part of the shell, but become smaller in passing to the posterior end. At the 

 summit of each main rib is a narrow, elevated, secondary rib, and on each side of 

 a main rib are two or three similar but rather small ribs. The secondary ribs are 

 separated by broad and rounded furrows. The summits of the secondary ribs 

 are usually sharp and even, but occasionally slightly serrate. 



Measurement* : 



Length . . . . . . . . 19 mm. 



Height 24 



Affinities. This form, of which I have seen one example only, agrees with the 

 specimen preserved in flint from Moreseat (Aberdeenshire) which was described 

 and figured by Salter as Lima elegans (Nilsson). That specimen is now in the 

 Museum of Practical Geology. Nilsson's 1 figure is scarcely sufficient to enable one 

 to determine the species, but from the recent illustrations given by Hennig 2 it is 

 seen that the British specimens differ from Lima elegans in being more distinctly 

 oblong and especially in having more numerous secondary ribs. 



1 'Petrif. Suecana' (1827), p. 26, pi. ix, fig. 7; Hisinger, ' Lethsea Suecica ' (1837), p. 55, pi. xv, 

 fig. 10. 



2 Revis. Lamellibr. i Nilsson's 'Petrif. Suecana' (1897), p. 33, pi. ii, figs. 9, 10, 11, 24; Lima 

 elegans, Dujardin (' Mem. Soc. geol. de France,' vol. ii, 1837, p. 226, pi. xvi, fig. 1), is apparently 

 distinct from Nilsson's species. 



