38 CRETACEOUS LAMELLIBRANCHIA. 



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

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



Ti/pf's. — From the Cambridge Greensand (indigenous), preserved in the Sedgwick 

 iMnsoum, Cambridge. 



liislriJiiifloK — Cauibridge (ircensaud (iii(bgoiinus). Lower Chalk of Burwcll. 



Til MA (Mantellum) liiMTAXxicA, sp. uov. Plate VI, figs. 13^^ — (L 



18-j7. Lima elegans, J. W. SaUer. Quart. Jouru. Geol. Soc, vol. xiii, p. 8.5, pi. ii, 



fig. 3 (non eJegans, Nilssou). 



Dc^criiiiion. — Shell moderately conA'ex, sub-quadrate or nearly oblong, very 

 oblique. Antero -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 

 car. Anterior area not distinctly limited, covered with ribs similai- 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 ril) are two or three similar Init rather small ribs. The secondary rilis are 

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

 are usually sharp and even, but occasionally slightly serrate. 



Measuremeutfi: 



Length 19 mm. 



Height 24 „ 



Afflvitirf^. — 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 Ijhna clrgans (Xilsson). That specimen is now in the 

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

 to determine the species, Init from the recent illustrations given by Hennig- 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. 20, pi. ix, fig. 7; Hisiuger, ' Lethsea Suecica ' (1837), p. 55, pi. xv, 



fig. 10. 



2 Eovis. Lamelllbr. i Nilsson's ' Petrif. Suecaua' (1897), p. 33, pi. ii, figs. 9, 10, 11. 2t; Lima 

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

 distinct from Nilsson's species. 



