SPIRIFER 361 



more conspicuous upon members of this species, although this may be due 

 to the difference in preservation. 



Horizon. Fern Glen formation and lower Burlington limestone. 



SPIRIFER GRIMESI Hall 

 Plate LI, Figs. 1-2 ; Plate LII, Figs. 1-4 ; Plate LIII, Figs. 1-2. 



1858. Spirifer grimesi Hall, Geol. Iowa, vol. 1, pt. 2, p. 604, pi. 14, figs. 1-5. 

 1883. Spirifera Grimesi Hall, Rep. N. Y. State Geol. for 1882, pi. (31) 56, 

 figs. 8, 16-19. 



1894. Spirifera grimesi Keyes, Mo. Geol. Surv., vol. 5, p. 79. 



1895. Spirifer Grimesi Hall and Clarke, Pal. N. Y., vol. 8, pt, 2, pi. 30, 



figs. 8, 16-19. 



Description. Shell large, varying from longitudinally to transversely 

 subelliptical in outline, the length sometimes greater but usually less than 

 the width, the hinge-line -snorter than the greatest width, the cardinal 

 extremities rounded or obtusely angular. The dimensions of two indi- 

 viduals, the smaller one the type of the species, are : length 88 mm. and 

 85 mm., width 100 mm. and 77 mm., thickness 61 mm. and 53 mm., length 

 of hinge-line 80 mm. and 52 mm., height of cardinal area 8 mm and 8 mm. 



Pedicle valve strongly convex, the greatest convexity posterior to the 

 middle, the surface sloping abruptly from the rather broad umbonal 

 region to the cardinal margin, and more gently to the antero-lateral 

 margins, sometimes a little compressed towards the cardinal extremities: 

 beak rather obtusely pointed and incurved; cardinal area of moderate 

 height, arched, the curvature becoming stronger towards the beak, some- 

 times almost flat towards the hinge-line, the lateral margins very sharply 

 defined, sloping from the beak to the cardinal extremities, the slope 

 becoming more abrupt distally, the delthyrium large, broader than high ; 

 lateral slopes convex, becoming more or less flattened towards the cardinal 

 extremities, covered with depressed, rounded, bifurcating plications; 

 mesial sinus rather broad and shallow, usually rounded but sometimes 

 somewhat angular in the bottom, originating near the beak where it is 

 rather sharply defined when the surface of the shell has not been eroded, 

 loosing its definition anteriorly, sometimes produced in front, into a 

 nasute or lingual extension, its surface covered with bifurcating plica- 

 tions like those on the lateral slopes. 



Brachial valve about as convex as the pedicle, the greatest convexity 

 near the middle; the lateral slopes convex, becoming somewhat com- 

 pressed towards the cardinal extremities, marked by depressed, rounded 

 plications like those of the opposite valve ; the mesial fold broad, rounded, 

 ill-defined, sometimes becoming strongly elevated and somewhat angular 

 towards the front, originating at the beak where it is scarcely or not 

 at all elevated above the general surface of the valve, marked with plica- 

 tions like those upon the lateral slopes of the shell. 



