No. 109.] 163 



Spirifer pertenuis ( n. s.). 



Pal. N.Y. Vol. iv. 



Shell extremely fragile, transversely oval, gibbous, about tliree- 

 fourtlis as* long as broad ; hinge equalling the greatest width of 

 the shell, more or less angular at the extremities according to 

 age : dorsal valve regularly convex ; mesial fold of medium 

 breadth, rounded and somewhat depressed above, sometimes 

 having a faint depression along the middle : ventral valve the 

 more convex, most prominent at the umbo, from which it 

 slopes abruptly with a slight convex outline to the front and 

 lateral margins; mesial sinus shallow, rounded, with faint in- 

 dications of plications; beak unknown; area moderately high, 

 more or less arcuate ; foramen higher than wide. Shell marked 

 by about twenty-three simple depressed and rounded plications 

 on each side of the mesial fold and sinus. Surface ornamented 

 by faint traces of fine irregular radiating striae, which are stud- 

 ded with fine granulations, and crossed by very fine, regular, 

 undulating, concentric lines of growth, arching gently upwards 

 on the mesial fold. 



This species is remarkable for the extreme tenuity of the shell. It differs 

 from the preceding species ( S. tenuis ) in the more conspicuous as well as 

 more numerous plications, and the less conspicuous concentric lines of 

 growth. The mesial sinus is more distinctly defined at the margins, and the 

 slight depression on the mesial fold differs extremely from the broader and 

 deeper one of the preceding species. In the last-named character, as well 

 as in its more numerous plications and more strongly defined mesial sinus 

 and fold, it differs very conspicuously from Spirifer arata. 



Geological 'position and locality. In the shales of the Hamilton group 

 near Cumberland, Maryland. 



Spirifer granulifera. 



Dclthyris granulifera, Bxii. -. Geol. Rep. 4th Dist. N.Y. 1843, p. 207, f. 1. 

 Delthyris congesfa, Hall : Idem. 

 An examination of a large number of specimens of the S. gra?mlifera, 

 in various phases of preservation, has convinced me of the identity of this 



