246 PALMONTOLOGY OF NEW YORK. 



This spc'i'ies is (listiiigiiislicd by its erect I'urm, the Ijruiul tlat interspaces 

 between the radii, and the regular sharp concentric striaB. 



Formation and locality. The specimen is I'roni the higlier t)eds of limestone 

 at the Falls of the Ohio, which arc of the age oftlic llainiltun Lumni. 



LlMlll'TKKA MACKDl'TERA. 



PLATE XXIV. FIU U, I'l.ATK XXVI, FIGS 0-9 ; I'LATE XXVU, FKiS 1-10; I'l-ATi; \X\1I1. FKiS 4, S ; I'LATE 



XXIX, FIGS. I-l ; AND I'LATE XCII, FIGS. 4-9 



Lima mne-riiptrrn, Co:<r.IlD. Annual Report N. Y tteolog'. Snrv., p. 117. 1S3S. 

 Limaplern inaj-rnptcin (Co.nkad), Hall. Prelim. Notice Lara. Shells, etc., pt. "J. p. 17. Dec, 1S69. 



S. A. Mii.i.ER, Cat. Amer. Pal. Fo.s.s. 1877. 



IIai.i.. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 24, fig. 14 ; 

 pi. 2I>, figs. 0-9 ; pi. 27, figs. 1-10 ; pi 28, fig.<. 4, .5 ; and pi. 29. 

 figs. 1-4. .Ian., 1883. 



Shell large ; including the cardinal expansions, the form is subquadrate ; body 

 broadly ovate, erect or moderately oblique ; wing more or less expanded ; 

 height one-fourth to one-third greater than the length ; basal margin broadly 

 rounded, with the anterior and posterior sides sub-parallel. 



Valves very uiu'<|ual. Left valve ranging from moderately convex to 

 very gibbous, often .somewhat regularly arcuate from Ijeak to base. Right 

 valve smaller than the opposite, in young specimens nearly tlat l)elow, 

 depressed-convex in the middle, and more convex in tlie umboual region; 

 iu specimens of medium size there is often a greater convexity in the upper 

 part, and in very old specimens the surface is depressed-convex ami nearly 

 flat in the lower part. 



Hinge-line straight, sometimes equalling but usually less than the length 

 of the .shell. 



Beak of the left valve proiuiueiit, acute, iiicliiHMl lorwanl, rising above and 

 arching over the cardinal line, situated anterior to the middle of the l)ody of 

 the shell. Umbonal region proiuiiient, convex in yuiuig shells and gibbous 

 in older ones, limited anteriorly l)y a distinct sulcus, and posteriorly Ijy the 

 abrupt umbonal slope. Beak of right valve acute, scarcely rising above the 

 hinge-line, defined anteriorly by the byssal sulcus, and posteriorly by the 

 abrupt depression and distinct limitation of the wing. Umbonal angle acute. 



