546 Contributions to Invertebrate Palaeontology. 



RECOGNIZED SPECIES FROM THE MARCELLUS SHALES OF OHIO. 



MOLLUSCOIDEA. 

 BRACHIOPODA. 



Genus LIXftlJLA Brug. 



Lriiigiila J^Iaiini. 



Plate XI, figs. 1 and 2. 



Lingida Manni Hall. ; 16tli Rept. State Cab. N. Y., p. 24; Pal. N. Y., vol. 4, 

 No. 6, pi. 2, fig. 3. 



Shell of medium size, longitudinally subovate, somewhat more than half as 

 wide as long, very obtusely pointed at the upper end, with subparallel lateral 

 margins, and often rather squarely truncate in front, with rounded basal angles. 

 Substance of the shell thin and polished, with irregular concentric lines of 

 growth which do not produce any marked surface character. Interior of the 

 valves sometimes characterized by a thin, hair-like, median ridge, which 

 extends to below the middle of the valve, leaving a distinct median depression 

 on the cast where the substance of the shell has been removed. 



The specimens of this species are usually about three-fourths of 

 an inch in lenj^th by a little less than half an inch in width. They 

 vary considerable in outline, the variation being principally in the 

 form of the front, some of them being much more round on the 

 front margin than others, or than the type specimens. This varia- 

 tion also causes a difference in the form of the lateral margins pro- 

 ducing a more rounded or oval form, and giving the shells an ap- 

 pearance approaching that of L. Delia Hall, Pal. N. Y., vol. iv, p. 

 12, pi. 2, fig. 9. The two forms are associated in the shales and 

 can scarcely be considered as distinct species. Many of the speci- 

 mens are so distinctly like L. Manni, that it seems impossible the 

 others having so slight a difference in form could be distinct, that I 

 have not thought it advisable to attempt their separation. 



