26 CRETACEOUS LAMELLIBRANCHIA. 



Anterior area lanceolate, depressed, limited by a sharp edge, ornamented with 

 radial ribs. 



Ornamentation consists of very numerous, small, somewhat flattened ribs, 

 separated by much narrower grooves. The ribs are usually wavy, and are not all 

 of equal size; posteriorly smaller ribs sometimes alternate with larger. The 

 grooves are punctate and vary somewhat in width. A few distinct growth-lines 

 are seen, below which the direction of the ribs may undergo some deflection. 



Measurements : 



(1) (2) (3) (4) (5) (6) 



Length . .37 35 31 23 21 20mm. 

 Height . . 62 58 56 37 35 32 



(1, 2, 3, 5) Lower Greensand, Upware. 



(4) Tealby Limestone, North Willinghain. 

 (6) Speeton Clay, Speeton. 



Affinities. Lima longa has a smaller apical angle and is relatively shorter than 

 L. undata, Deshayes 1 ; it is also clearly distinguished by the absence of the prominent 

 concentric scales, and by the occurrence of pits in the grooves. 



Remarks. In some cases, especially when the specimens are not perfectly 

 preserved, the ribs (as remarked by Wollemann) become indistinct on the middle 

 of the shell. This is the case in specimens from the Tealby Limestone, and in some 

 from the Speeton Clay, in which the middle part of the shell is almost smooth. 

 The outline of the shell and the relative size of the posterior ear are rather variable. 



A specimen from West Dereham (Plate V, fig. 13) possesses finer ribs, but may 

 perhaps be only a variety of this species. 



Types. From the Hilsthon of Elligser Brink. A specimen from the same 

 locality (imperfect on the posterior side of the umbo) is figured by d'Orbigny and 

 is preserved in the Museum of Palaeontology at Paris. Two of the specimens from 

 Upware figured by Keeping are in the Sedgwick Museum, Cambridge, and another 

 is in the collection of Mr. J. F. Walker. 



Distribution. Lower Greensand of Upware, Potton, and Brickhill. Tealby 

 Limestone (zone of Belemnites brunsviceiisis) of North Willingham. Upper part of 

 Speeton Series of Speeton. 



LIMA (ACESTA) CLYPEIFOEMIS, d'Orbigny, 1847. Text-figure 5. 



1847. LIMA CLYPEIFORMIS, A. d'Orbigny. Pal. Fran9- Terr. Cret., vol. iii, p. 543, 



pi. ccccxvii, figs. 9, 10. 

 1850. d'OrUgny. Prodr. de Pal., vol. ii, p. 166. 



1 See d'Orbigny, p. 528, pi. ccccxiv, figs. 9 12 ; Pictet and Campiche, p. 133, pi. clxii, fig. 1. 



