434 PALEONTOLOGY OF NEW YORK. 



LUNULICARDIUM, Munster. 1840. 



LUNULICARDICM FRAGILE. 



PLATE LXXl, FIGS. 1-U. 



Av'tculafragUix, Hah. Geol. Suiv. N. Y., Rep. Fourth Dist., p. 222, t. 94, figs. 1, 2. 1842. 

 Arirulopecten frttffilis (Hall), S. A. Milluk. Cat. Am. Pal. Foss., p. 184. 1877. 

 Lunulicardium fragile. Hall. Pi-elim. Notire Lamellibraiichiata, 2, p. 97. 1870. 



" " " PaLN. Y., vol. V, pt. 1. Plates and Explanations: PL 71, figs. 1-14. 1883. 



Shell small, short, obovate, and more or less variable in form ; abruptly atten- 

 uate above ; length a little greater than the height ; basal and anterior mar- 

 gins regularly rounded. Po.sterior side obliquely truncate and margined by 

 a thin expansion of the shell. 



Valves, in their natural condition, moderately convex in the lower part, 

 and a little gibbous in the umbonal region, but u.sually much compressed 

 where occurring in the soft shales. 



Beaks attenuate, erect. 



Surface marked by fine concentric striae, and in well-preserved specimens 

 by extremely fine radiating striae, which are sometimes more strongly 

 marked on the posterior portion of the shell. 



Three specimens measure respectively 8, 10 and 12 mm. in length, and 8, 

 9 and 11 mm. in height. 



The shells are small and fragile, and usually occur in great numbers in cer- 

 tain layers of the Marcellus shale and Genesee slate. These fossils are usually 

 deprived of the thin expansion bordering the hiatus on the posterior side, the 

 presence of which is shown in figs. 4, 8, 13 and 14 of plate Ixxi. 



Formations and localities. Common to the Marcellus shale, Hamilton group, 

 Genesee slate and Portage group ; also found sparingly in the Chemung group, 

 N. Y. It has likewise been noticed in the Genesee slate of Ohio and Indiana. 



