SPIRIFER 345 



SPIRIFER LEIDYI Norwood and Pratten 

 Plate XL VII, Figs. 17-31 



1855. Spirifer Leidyi Norwood and Pratten, Jour. Acad. Nat. Sci. Phil., 



(2), vol. 3, p. 72, pi. 9, figs. 2a-c. 

 1883. Spirifera Leidyi Hall, Rep. N. Y. State Geol. for 1882, pi. (30) 55, 



tigs. 25-26. 

 1894. Spirifer Leidyi Hall and Clarke, Int. Study of Brach., pt. 2, pi. 27, 



figs. 16-17. 



1894. Spirifera leidyi Keyes, Mo., Geol. Surv., vol. 5, p. 82. 



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



figs. 25-26. 



Description. Shell below medium size, wider than long, the greatest 

 width usually along the hinge-line, the cardinal extremities angular or 

 rarely a little rounded, the valves subequally convex. The dimensions of 

 two individuals are: length 21 mm. and 17.8 mm., width 27.5 mm. and 23 

 mm., thickness 15 mm. and 14.5 mm. 



Pedicle valve with its greatest convexity posterior to the middle, the 

 beak pointed and incurved ; cardinal area concave, becoming more curved 

 towards the beak, its height 2 to 3 mm., its inferior portion sloping pos- 

 teriorly at an angle of about 115 degrees to the plane of the valve, the 

 lateral margins sharply defined, sloping from the beak to the cardinal 

 extremities in either a straight or gently curved line; lateral slopes of the 

 valve convex, becoming a little compressed towards the cardinal extremi- 

 ties in the broader individuals, the surface curving more abruptly to the 

 cardinal than to the antero-lateral margins, each lateral slope bearing 

 from 7 to 10 angular plications, 8 being the more usual number, which 

 grow gradually smaller towards the cardinal extremities, the second pli- 

 cations on each side, those next to. the bounding plications of the sinus, 

 originate near the beak from the outer side of the first plications, the 

 remaining ones extend to the cardinal margin and are usually simple, 

 although occasionally one of the larger ones, more often the fourth, bifur- 

 cates near the beak and gives origin to the third plication from its inner 

 side; the mesial sinus originates at the beak where it is angular and 

 sharply defined, becoming rather profound anteriorly, an angular median 

 plication originates close to the beak and continues to the anterior 

 margin with gradually increasing size, each of the lateral bounding pli- 

 cations gives rise, from its inner side near the beak, to a single plication 

 which continues without division to the anterior margin; these lateral pli- 

 cations never attain the strength of the median one, they are much smaller 

 and occasionally are nearly or quite obsolete. 



Brachial valve equally or a little less convex than the pedicle, its great- 

 est convexity near the middle, the surface curving more abruptly to the 

 cardinal margin, usually becoming somewhat compressed towards the 



