Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/588

502 502 A. J. JUKES-BROWNE'S SUPPLEMENTARY

specimen in the Woodwardian Museum presents the characters above mentioned. The ribs are strongly marked on the casts ; the shell varies in length from 13 to 17 lines. D'Orbigny gives it as a Turonian form ; but it appears also to occur in the Gault Superieur of Cheville (' Renevier,' p. 163).

Lima Rauliniana, D'Orb.

Lima Rauliniana, D'Orb. Pal. Fr. iii. pi. ccccxvii. figs. 5-8.

This species bears a considerable resemblance to Lima aspera, Mant. : and the Cambridge specimens have hitherto been confounded with that form.

Great differences, however, are discovered on a close examination. L. aspera has wide, flattened ribs, separated by very narrow inter- spaces, mere grooved lines, in fact, which are pitted at intervals.

L. Rauliniana has low rounded ribs with peculiar imbrications, and the interspaces are nearly as wide as the ribs. M. d'Orbigny's description is correct so far as it goes ; and fig. 7 shows the peculiar ribs " sur lesquelles sont comme des tuiles obliques en dehors, espacees ot alternes ;" he does not, however, mention the ornamen- tation of the interspaces ; these are not pitted, but crossed with irregular transverse grooves or striations, very minute and closely set.

The main characters of the shell may be thus described : — valves nearly equal and equiconvex, each bearing between 40 and 50 low rounded ribs, interrupted occasionally by the lines of growth ; the ribs are ornamented with elongate imbrications, projecting slightly over their inner side, viz. over the left side of one half of the ribs, and over the right side of the other half, on each side of a median line, where the ribs divaricate ; when worn, the ribs appear to be simply notched ; the interspaces are grooved in the way above mentioned.

The specimens are generally preserved in the lighter-coloured phosphate, which at one time I thought had been formed in situ : I have since, however, been led to think that these phosphates have also been derived, but probably from rather higher beds of the Gault than those from which most of the black nodules came.

Lima Rauliniana is found in the Gaize or Gault Superieur of the Paris basin ; and casts of similar shape are quoted from Cheville by Prof. Renevier (Taune de Cheville,' p. 163) ; but I am not aware that it has been previously discovered in England.

Lima interlineata, new sp. PI. XXI. fig. 10.

Shell transversely oval, or obliquely quadrate : valves equiconvex, and each ornamented with 10 or 11 strong rounded ribs radiating from the umbo ; interspaces wide and flat, marked with a few distinct longitudinal lines, which vary in number from 1 to 5, but are most numerous on the more central interspaces. There appear to have been several stronger striae or small ribs on the anterior side or buccal region ; but the shell is here worn off.