LIMA. 13 



Description. — Sliell moderately convex, oval, liit^licr than long, venti-al and 

 posterior margin rounded. Umbone.s sharp. Apical angle about 80°. Anterior 

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

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

 anterior ear. 



Ornamentation consists of about 52 flattened ribs, slightly undulating, 

 separated by very nari-ow grooves Avitli 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 „ 



-Ufiiiitics. — This is distinguished from L. rillerseiisis (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 157-ji. 



Didrihnfiiiii. — Lower Greensand (Ferruginous Sands) of Shanklin. 



LiM.v (Plagiostojia) viLLiousKNsis? I'ictct uiul Cuiiijuclu', 18G'J. i'lale ill, ligs. Ihi, 



Ul>,l2<i,b,r3. 



? 1869. Lima villersensis, F. J. Pictet and G. Campiche. Foss. Terr. Crt't. Ste. 



Croix (Mati'r. 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 8-5°. 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. 



Ui'nameutation consists of from o2 to ^G broad, flattened, nearly straight ribs, 

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

 near the posterior border, the riljs l)econie narrower. A few well-marked growth- 

 ridges may occur at distant intervals. Near the ventral mai-gin 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 . 10 . 18 . II nun. 



Height . 2G-.J . 2.5 22 . 17 „ 



(1 — 4) Lower GreeusauJ, i'ariugJou. 



