^t- 



LINGUL^ OF THE HAMILTON GROUP. 9 



Lingula leaiia ( n. s.). 



PLATE n. 

 Shell robust, ovate, subattenuate towards the beak ; margins gradually 

 expanding and curving from the beak for about two-thirds the length, 

 where the shell has its greatest width. Lower half of the shell very 

 depressed - convex, becoming more convex towards the beak. Shell 

 comparatively thick, lamellose. 

 Surface marked by fine concentric striae and faint interrupted radiating 

 striae, which are more conspicuous and continuous in the exfoliated 

 shell. The length of an apparently full grown individual is eight-tenths 

 of an inch, and the greatest width eleven-twentieths of an inch. 

 This species is conspicuously distinct from any others in the Hamilton and 

 Chemung groups, except L. palaformis, from which it differs in its greater propor- 

 tional length and more attenuate form towards the beak. So far as known to me, it 

 is a rare species. 



Geological formation and locality. In some calcareous layers in the Hamilton 

 shales, in Bristol, Ontario county, N.Y. 



Lingula iiiaida ( n. s.). 



PLATE IL 



Shell linguiform, elliptical, greatest width a little more than half the 

 length, narrowing gently towards either extremity, obtusely rounded 

 and produced below, and more acutely converging towards the beaks. 



Surface very gently convex below and a little more convex on the umbo, 

 marked by fine threadlike striae which are sometimes crowded in fa- 

 scicles. No radiating striae are preserved in the specimen. 

 The specimen described is apparently a ventral valve, and preserves some remains 



of the muscular impression. In form it resembles the L. ligea, but is less convex, 



and the lower part of the shell is more produced, so that the strise make a more 



extended curve than on that species; and they are likewise coarser. 



The typical forms of L. ligea are about half an inch in length and one quarter of 



an inch in width; and the L. maida has a length of more than three-fourths of an 



inch, with a widih of nearly l)alf an inch. 



Geological formation and locality. In the Moscow shales of the Hamilton group : 



at Moscow, N.Y. 



[ Palxontolooy IV.] 2 



