LIMA. 



11 



right uiigle. Uml)ones of moderate size. Area large, with a hirge 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 witli numerous (43 to 52) radial ribs, which are straight or 

 slightly undulating. The ribs are flattened; near the uml)o they are separated by 

 Tuxrrow 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 {Plaijiostoma) subrigida, Romor. C'laxby Ii-onstono, lionuiwortli Haven. Right valve. 



Natural size. Sedgwick Museum. 



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

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

 Measurements : 



(1) (2) (3) 



Kt'.i 100 80 



111 1 08 85 



— (J3 — 



48 49 48 



On 



Length 

 Height 

 Thickness 

 Number of riljs 



(1 — 9) Claxhy IroustoiK', Beuuiworth Haveu. 



Affinities. — L. rii/nrnlriisis, Pictet and Campiche,' is distinguished from 

 L. subrigida by its more (luadrilateral outline, more luunerous ril)s and finer 

 > 'Ton-. Civt. Ste. Croix' (1869), p. 138, \A. clxii, fiijs. 5—8. 



