TRENTON LIMESTONE. 181 



Position and locality. In the higher shaly part of the limestone at Adams, Jefferson 

 county, and Turin, Lewis county. 



235. 12. MURCHISONIA VITTATA (w. s;j.). 



Pl. XXXIX, Figs. 3 a, b. 



Elongated, fusiform, slender ; volutions oblique, scarcely vcntricose, last one moderately 

 expanded ; suture apparently banded ; aperture extremely elongated. 



This species has the volutions as oblique as the preceding, and differs principally in the 

 less expansion of the lower one, and the more elongated aperture. The suture appears to 

 be banded, but the single specimen seen is a cast, and this character is somewhat obscure. 

 In general characters, the two last more nearly resemble Loxonema than Murchisonia ; 

 but never having seen the former genus well characterized in the Lower Silurian strata, I 

 am unwilling to admit it upon the evidence of a cast alone. 



Fig. 3 a. View of the back of the spire. . 



Fig. 3 6. A partial front view, showing a part of the aperture. 



Position and locality. In the higher shaly layers of the limestone at Adams, Jefferson 

 county. ^ ,/ .. 



236. 13. MURCHISONIA GRACILIS (71. *;;.). 



Pl. XXXIX. Figs. 4 a, J, c. "" ' 



Slender, elongated ; volutions not less than ten, ventricose, subangulated on the middle, 

 very gradually increasing in size from the apex towards the aperture ; surface marked by 

 a carinal band upon the centre of the volution, with curving striis above and below. 



This is the most slender species known in the rock. It is quite distinct from either of the 

 preceding, in the gradual enlarging of the volutions, and its uniformly small size. The 

 centre of the volutions is distinctly marked by an obtuse carina, giving them a subangular 

 character quite different from the M. hellicincta. Casts of the shell are entirely free from 

 the angular carina. 



All the specimens seen in the limestone of New- York are of the size of those figured, 

 and preserve, but imperfectly, the shell. It is quite similar to, and perhaps identical with, 

 the slender species found in western localities, but is entirely distinct from M. angusta of 

 the Birdseye limestone. ■ . 



Fig. 4 a. Fragment showing six volutions. 



Fig. 4 b. Another fragment, showing one of the lower volutions partially covered by the shelL 



Fig. 4 c. A small fragment, on which the shell is partially preserved. 



Position and locality. In the crystalline portions of the Trenton limestone at Watertown 

 and Middleville in New- York, at Carlisle in Pennsylvania, and also in the lower shaly 

 beds at Middleville. 



