Fauna of the Morrow Group 
219 
perpendicular to hinge-line, 35.4 mm. ; convexity of left valve, 
about 12.5 mm.; length of hinge-line, 16.5 mm. 
Left valve strongly but irregularly convex, the greatest infla- 
tion occurring at a point a little below the umbo and in front 
of the middle, surface of the valve curving very abruptly to the 
anterior lateral margin and toward the auriculations but more 
gently toward the ventral and posterior margins ; ears small and 
poorly deflned, outline of valve very slightly notched beneath 
anterior ear but not beneath posterior one; beak small but full, 
situated back of the middle of the hinge-line and directed some- 
what posteriorly; margins of the valve probably irregular and 
somewhat variable, in type specimen posterio-ventral . margin 
slightly concave and posterior margin produced and strongly 
convex ; surface of internal cast ornamented by strong, irregular, 
rounded, radiating ribs originating beyond the umbo and in- 
creasing in strength toward the margin, which display a ten- 
dency toward becoming nodose and are crossed by faint, irregu- 
lar, concentric lines of growth. 
Right valve and ornamentation of shell surface unknown. 
Remarks. This species is based upon an internal cast of a 
left valve from the Kessler limestone and differs markedly from 
the members of this genus described from the Coal Measures 
in its greater inflation and peculiar outline. 
Horizon and locality. Kessler limestone : East Mountain, Fay- 
etteville, Arkansas (Station 209), 
MYALINID^ 
Genus MYALINA De Koninck 
Myalina recur virostris Meek & Worthen 
18’60. Myalina recurvirostris. Meek and Worthen, Proc. Acad. Nat, Sci., 
Phil., p. 456. 
Coal Measures: Near Springfield, Illinois. 
18'66. Myalina recurvirostris. Meek and Worthen, Geol. Surv. 111., vol. 2, 
p. 344, pi. 26, figs. 9a-c. 
Upper Coal Measures: LaSalle, Illinois. 
1884. Myalina recurvirostris. White, 13th Rep. Geol. Surv. Ind,, p. 140, 
pi. 29, figs. 3, 4. 
Upper Coal Measures: Indiana. 
1894. Myalina recurvirostris. Keyes, Mo. Geol. Surv,, vol. 5, p. 117, pi. 
45, figs, la, b. 
Upper Coal Measures. 
