PELECYPODA—PRIONODESMACEA. 



389 



XX. Fordilla Barrande. 

 Minute, thick, oval. Hinge margin nearly straight. Surface 

 concentrically striated. 



This may be a bivalve crustacean allied to Estheria. Cambric. 



45. F. troyensis Barrande. (Fig. 495.) Cambric. 



Lower Cambric of southeastern New York, eastern Massa- 

 chusetts 



Fig. 495. Fordilla troyensis, right valve and right internal mold, enlarged. (U. 



S. G. S. , Ann. 10.) 



XXI. Panenka Barrande. 



Equivalve. Length and height nearly equal. Beaks prominent 

 and incurved. Hinge line straight or 

 arcuate. Shell thin, marked by growth 

 lines and usually by strong radii. 

 Siluric-Devonic. 



46. P. canadensis Whiteaves. 



Siluric. 



Subcircular to longitudinally subo- 

 vate ; umbones prominent, surface with 

 numerous ribs. 



Upper Monroe of Michigan, Ohio 

 and Canada. 



47. P. dichotoma Hall. (Fig. 496.) 



Devonic. 

 Convex below, gibbous above. Hinge line short and straight. 

 Schoharie : New York. 



48. P. ventricosa Hall. (Fig. 497, a-b.) Devonic. 

 Distinguished by its subcircular form, straight hinge line, ex- 

 tremely ventricose valves, prominent, subcentral beaks and nu- 

 merous, fine and close radii. 



Agoniatite limestone of Marcellus shale : New York. 



Fig. 496. Panenka dichotoma. 

 (Pal. N. Y., V.) 



