FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 105 



beyond width of beaks at their base. Surface marked by fine concentric striae, 

 usually obscured by the covering of minute, hair-like spines, which, when 

 removed, leave a punctate surface. 



Formation and Locality. Occurs abundantly at Waldron, Indiana, and rarely in the quarries 

 east of Louisville ; in the Niagara limestone of both places. 



Genus Spirifera. 



^~ Spirifera, Sowerby. Min. Couch., Vol. II. 1815. 

 Etymology: spira, a spire; fera, to bear. 



Shell structure fibrous and impunctate ; form very variable, but typical; 

 more or less three-sided or quadrate, sometimes oval or sub-circular. Hinge- 

 line straight, mostly as long as, or longer than greatest width of shell, 

 sometimes shorter. The cardinal angles sometimes obtusely rounded, more 

 commonly produced and extended, sometimes greatly so. Surface usually 

 with radiating ribs, or smooth or striated. Generally an elevated fold in one 

 valve, and a corresponding sinus in the other. Valves articulated by teeth 

 and sockets. Ventral valve the larger, with a more or less prominent beak, a 

 well marked area and a triangular foramen, which is sometimes closed by 

 a pseudo-deltidium. Dorsal valve with a narrow area, and a wide triangular 

 foramen. Interior more or less occupied by two spirally rolled lamellae, form- 

 ing two cones, the apices of which are directed towards the cardinal angles. 



Spirifera acuminata. CONRAD. 



Plate VIII., figures 1 to 8. 



Delthyris acuminata, Conrad. Ann. Rep. of Pal. of N. Y., p. 65 1839. 

 Spirifera acuminata, Conrad. Hall in 10th Rep. on State Cab., p. 135 1857. 

 Spirifera acuminata, Hall. Pal. N. Y., Vol. IV., p. 198, plate 29. 



Shell large, ventricose, transverse, with the hinge-line usually less than width 

 of shell ; cardinal extremities rounded or truncate, having a sub-elliptical or 

 sub-quadrate outline ; mesial fold and sinus extreme. Surface plicated. Ven- 

 tral valve variably convex on two sides, with a wide mesial sinus, which is well 

 defined in the upper part, becomes wider and deeper and less distinctly de- 

 fined in middle of shell, and is produced in front into a long triangular exten- 

 sion, curving abruptly from the greatest convexity to sides and cardinal 

 angles ; umbo prominent, with the apex incurved over the wide triangular fis- 

 sure ; area extending to cardinal angles, with margin rounded except towards 

 the extremities. 



Dorsal valve gibbous, highly elevated in middle into a strong angular mesial 

 fold, and curving from sides of fold to margin of shell, except at the cardinal 



UEOL. SUK. 14 



