LINGULiE OF THE HAMILTON GROUP. * 

 LIXGUL^ OF THE HAMILTON GROUP, 



IKCLVDINO THS IIABCEI.I.US SHAI.S. 



Lingula exilis. 



PLATE I. 

 Lingula exilit : Hall, Thirteenth Report of the Begents on the State Cabinet, 1860, p. 76, f. 2. 



Shell broad-ovate, moderately convex, length little greater than the 

 width ; apex obtuse ; cardinal margin obtusely rounded ; sides regu- 

 larly curving ; base broadly rounded. Surface lamellose, with irregular 

 rugse or lines of growth. 



The specimens obtaiued are imperfect at the beak, or in some other part. The 

 shell is very broad ; and the great width at the apex, and broadly rounded cardi- 

 nal extremity, distinguish it from all other forms of the Hamilton groujj, or of 

 the rocks of New- York. In the normal condition, the umbo appears to have been 

 quite prominent ; but the specimens occurring in the thinly laminated strata are 

 much flattened. 



It is associated with DisciXA and Conularla, similarly with those of the Ti"en- 

 ton group in New- York. 



Geological formation and locality. In the MarccIIus shale, near Bindgcwater ; 

 and an imperfect specimen has been found in the shales of the central part of the 

 Hamilton group, in Schoharie county, New-York. 



Liii^ulii ligea. 



PLATE L 

 Lingula ligea : Hall, Thirteenth Report of the Regents on the State Cabinet, 1800, p. 76. 



Shell narrow elliptical ; length equal to twice the width ; sides regu- 

 larly curving; extremities subequal ; margins of the valves thickened. 

 Surface marked by fine concentric striae, and by a few obscure or obso- 

 lete radiiiting strias. The more convex valve shows, along the inner 

 margin, a narrow shallow groove as if the edge of the opposite valre 

 closed just within its margin. 



