LIMA. 



11 



right angle. Umbones of moderate size. Area large, with a large triangular 

 ligament pit near the middle but bending posteriorly. Anterior area large, deeply 

 depressed, especially near the ears. Ears rather large, the anterior triangular, the 

 posterior rather larger, more elongate ; surface with growth-lamellae only. 



Surface ornamented with numerous (43 to 52) radial ribs, which are straight or 

 slightly undulating. The ribs are flattened ; near the umbo they are separated by 

 narrow grooves, but in passing ventrally the grooves increase in width and become 

 as wide as or wider than the ribs. The grooves are rather shallow and rounded. 

 The anterior and posterior ribs are narrower than the others. Near the umbo the 

 grooves are punctate, but in passing ventrally the pits soon become replaced by 



Fio. 2. Lima (Plagiostoma) subrigida, Romer. Claxby Ironstone, Benniworth Haven. 



Natural size. Sedgwick Museum. 



Right valve. 



transverse furrows separated by ridges, and the latter may pass on to the ribs. On 

 the anterior area ribs are small or absent, but growth-lines are usually distinct. 

 Measurements : 



(1) (2) (3) (4) (5) (6) (7) (8) (9) 



109 100 80 73 72 64 63 38 31 mm. 

 114 108 85 79 76 65 65 36 40 



63 36 



48 49 48 51 46 43 52 52 44 

 (1 9) Claxby Ironstone, Benniworth Haven. 



Length 

 Height 

 Thickness 

 Number of ribs 



Affinities. L. vignculensis, Pictet and Campiche, 1 is distinguished from 

 L. subrigida by its more quadrilateral outline, more numerous ribs and finer 

 1 'Terr. Oct. Ste. Croix' (1869), p. 138, pi. clxii, figs. 58. 



