LIMA. 13 



Description. Shell moderately convex, oval, higher than long, ventral and 

 posterior margin rounded. Umbones sharp. Apical angle about 83. Anterior 

 area depressed, limited by a rounded edge, ornamented with ribs. Ears with 

 distinct growth-ridges. Posterior ear higher than long, and larger than the 

 anterior ear. 



Ornamentation consists of about 52 flattened ribs, slightly undulating, 

 separated by very narrow grooves with pits. Near the ventral margin the ribs 

 become divided by a median groove. Near the anterior and posterior margins 

 the ribs are rather narrower than elsewhere. A few moderately distinct growth- 

 lines occur. 



Measurements : 



Length .... 20 mm. 



Height .... 25-5 



Affinities. This is distinguished from L. villersensis (see below) by its more 

 numerous and narrower ribs. 



Remark. I have seen one specimen only, which is preserved in the British 

 Museum, No. L 15754. 



Distribution. Lower Greensand (Ferruginous Sands) of Shanklin. 



LIMA (PLAGIOSTOMA) VILLERSENSIS ? Pictet and Campiche, 1869. Plate III, figs, lla, 



13. 



? 1869. LIMA VILLEBSENSIS, F. J. Pictet and G. Campiche. Foss. Terr. Oct. Ste. 



Croix (Mater. Pal. Suisse, ser. 5), 

 pp. 127, 162, pi. clxi, fig. 5. 



Description. Shell moderately convex, oval, higher than long, ventral and 

 posterior margins rounded. Umbones sharp. Apical angle about 85. Anterior 

 area depressed, bounded by a sharp edge. Posterior ear larger than the anterior, 

 higher than long, with the outer angle obtuse, and with a few radial ribs. 



Ornamentation consists of from 32 to 36 broad, flattened, nearly straight ribs, 

 separated by linear grooves with distinct pits. Near the anterior, and sometimes 

 near the posterior border, the ribs become narrower. A few well-marked growth- 

 ridges may occur at distant intervals. Near the ventral margin of the valves 

 (ventral to a growth-ridge) the position of the ribs is sometimes slightly shifted, 

 and the number of ribs may increase owing to the fission of some. 



Measurements : 



(1) (2) (3) (4) 



Length . 20 . 19 . 18 14mm. 



Height . 26-5 25 . 22 . 17 



(1 4) Lower Greensand, Faringdon. 



