52 CRETACEOUS LAMELLIBRANCHIA. 



strong ridges placed concentrically and regularly. Below a growth-ring the 

 ridges are sometimes situated more closely together. One or two ribs at the 

 margins of the ribbed area are rather smaller than the others. The parts between 

 the ribbed area and the anterior and posterior margins of the valve are smooth 

 except for faint growth-lines. 

 Measurements : 



Length 

 Height 



(1) Chalk, Clayton. 

 (2 5) A. quadratus zone, Winchester. 



Affinities. This species is distinguished from L. decussata (p. 50) by being 

 more pointed dorsally, by having fewer ribs, which also are rounded and confined 

 to the median part of the valve, and by the strong ridges which extend across the 

 ribs. 



In outline this species resembles Lima pectinata, d'Orbigny, 1 but differs in 

 having fewer ribs, in the absence of ribs on the anterior and posterior parts of the 

 valves, and in the ribs not being carinated and having ridges across them 

 instead of tubercles at the summits. 



This species resembles closely the form figured by Geinitz 2 as L. semisulcata, 

 Nilsson. 



Distribution. Zone of Actinocamax quadratus of Winchester. Upper Chalk 

 (probably zone of Micraster cor-testudinarium) of Kenley. 



LIMA (LIMATULA), sp. Plate VII, fig. 23 a, b. 



Description. Shell inflated, oval, nearly equilateral. Umbones small. Hinge- 

 line relatively long. Ears not sharply limited, nearly equal. 



Ornamentation consists of about 20 narrow ribs, separated by very broad and 

 shallow interspaces in which very fine radial ribs may be seen. The ribs anterior 

 to the median line are closer together and rather stronger than the others. On 

 the parts of the valves next to the ears ribs appear to be absent. 

 Measurements : 



Length ........ 6*5 mm. 



Height 9 



1 'Pal. Fran9. Terr. Cret.,' vol. iii (1847), p. 572, pi. ccccxxvii, figs. 1519. 



2 Das Elbthalgeb. in Sachsen,' pt. 2 (1873), p. 53, pi. xvi, fig. 14. 



