LIMA. 9 



Anterior ears triangular, rather small ; posterior ears obtusely triangular, elongate, 

 with radial ribs. 



Valves ornamented with numerous flattened ribs arranged on either side of a 

 line passing from the umbo to the ventral margin, from which they diverge slightly. 

 The ribs are nearly straight or slightly undulating, but are often bent abruptly 

 where they cross growth-lines. Surface of ribs nearly smooth, but sometimes 

 showing very fine concentric ridges or (when worn) oblique striae. On the inner 

 edge of each rib that facing the middle line there are short, slit-like indentations, 

 above each of which a short spiny projection is seen in perfectly preserved 

 specimens. These slits and spines do not, as a rule, show a concentric arrange- 

 ment. The grooves separating the ribs are very narrow and are marked with 

 pits near the umbo and with transverse grooves ventrally. Sometimes near the 

 margins of the valves new ribs are intercalated or old ones bifurcate. 



Measurements : 



(1) (2) (3) (4) (5) (6) (7) 



Length .... 31 . 30 . 28 . 26 . 24 . 19 . 16 mm. 

 Height . . . . 36 . 33 . 33 . 35 . 26 . 23 . 21 

 Number of ribs . 66 . 41 r 60 . 46 . 42 . 41 . 52 

 (1, 2, 3, 7) Totternhoe Stone, Burwell. 



(4) Cherry Hinton. 



(5, 6) Chalk Marl, Folkestone. 



Affinities. The Senonian form figured as Lima aspera by Goldfuss, Reuss, and 

 Fritsch is clearly distinguished from this species by the chevron-like ornamentation 

 on the ribs. Pictet and Campiche suggest that Goldfuss' species may be identical 

 with Lima Dunkeri, Hagenow, 1 from Riigen, but this view is not supported by the 

 figures given by Vogel and Ravn. The form figured by d'Orbigny has a larger 

 apical angle than L. aspera, Mantell, and does not show the spiny projections on 

 one side of the ribs. 



The example figured by Reuss 2 as Lima plana is similar in form to L. aspera, 

 Mantell, but does not appear to possess the spiny projections on the ribs. 



Types. I have not been able to find the types. 3 They came from the Chalk 

 Marl of Hamsey and Stoneham. 



Distribution. Chloritic Marl of Eastbourne. Chalk Marl of Folkestone, and 

 Blue Bell Hill (Burham). Totternhoe Stone of Arlesey, Burwell, Cherry Hinton, 

 and Stoke Ferry. 



1 'Neues Jahrb. fur Min.,' etc. (1842), p. 556. 



2 ' Verstein. bohmisch. Kreideformat.' (1846), p. 35, pi. xxxviii, fig. 20. 



3 The name aspera was used by Chemnitz (1784) for a recent species of Lima, but since that has 

 been shown to be a synonym of Lima scabra (Born, 1780) there does not appear to be sufficient reason 

 for giving a new name to the Chalk species which, for over eighty years, has been known as Lima 

 aspera, Mantell. 



2 



