2r> ("RKTACKOUS LA]\rKI.Ln?R.\X('ll I.\. 



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

 radial ribs. 



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

 separated by much narrower gi'ooves. 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 sonieAvhat 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) 



Length . .37 35 31 23 



Height . . G2 58 5G 37 



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



(4) Tcalby Limestone, North Willinghain. 



(6) Speetou Clay, Speetou. 



Ajfinities. — Lima loiujn has a smaller apical angle and is relatively shorter than 

 L. undnta, Deshayes ' ; it is also clearly distinguished by the absence of the proiiiiiit'iit 

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



licmarks. — 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 iniddle ])art of the shell is almost smooth. 

 The outline of the shell and the I'elative 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. 



Tjipes. — From the Ililsthon of EUigser Brink. A specimen from the same 

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

 is preserved in the Museum of Palaeontology at Paris. Two oF the sj^'cimeiis from 

 Upware figured by Keepuig are in the Sedgwick Museum, Cambridge, and auotiier 

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



JJistribulioii.—hovfev Greensand of Upware, Potton, and Priekhill. Tealby 

 Limestone (zone of JJdemnites brans oicensis) of North Williughani. Ujiper part of 

 Speeton Series of Speeton. 



TiiMA (Acksta) CLYPElFOKMis, (VOrJihjii ij, 1817. Text-figure 5. 



1847. Lima clypehokmis, A. d'Orhiijiitj. Pal, Fraiu;. Terr. Crt't., vol. iii, p. 543, 



pi. ecccxvii, figs. 9, 10. 

 1860. — — d'Orbigny. Prodr. de Pal., vol. ii, p. 166. 



^ See d'Orbiguy, p. 528, pi. ccccxiv, figs. 9 — 12 ; Pictet aiid Campiche, p. 133, pi. clxii, fig. 1. 



