340 MISSISSIPPIAN BRACHIOPODA 



The minute surface markings of all the specimens observed are nearly 

 obliterated by the silicification of the shell, but at a few points very fine 

 longitudinal strias are preserved. It is not possible to determine whether 

 or not the surface is also covered with fine, concentric markings of any 

 sort. A few concentric lines of growth are present. 



Remarks. This species is quite distinct from any other members of the 

 genus Spirifer in our Mississippian faunas. In its minute surface markings 

 it seems to be like the large 8. grimesi and 8. logani, though this cannot be 

 stated with certainty because of the poor preservation of these characters. 

 In its general form the species is perhaps more nearly like some examples 

 of 8. increbescens than any other, but the valves are much less convex, the 

 cardinal area is flatter and lies in a very different plane, and the strong 

 median plication of the sinus is a characteristic feature. 



H or izon. Upper Keokuk limestone. 



SPIRIFER PELLAENSIS n. sp. 

 Plate XLV, Figs. 1-31 



1858. Spirifer keokuk var. Hall, Geol. Iowa, vol. 1, pt. 2. p. 676, pi. 24, 



figs. 4a-d. 

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



figs. 23-24 (not figs. 21-22). 

 1891. Spirifer Rocky montana? \\ 7 hitfield, Ann. N. Y. Acad. Sci., vol. 5, p. 



584, pi. 13, fig. 20. 

 1895. Spirifera Rcckymontanaf Whitfield, Geol. Surv. Ohio, vol. 7, p. 471, 



pi. 9, fig. 20. 

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



figs. 23-24 (not figs. 21-22). 

 1897. Spirifer keokuk Weller, Trans. N. Y. Acad. Sci., vol. 16, p. 257, pi. 



18, figs. 10-12. 

 1911. Spirifer keokuk Morse, Proc. Ohio Acad. Sci., vol. 5, p. 377, fig. 11. 



Description. Shell below medium size, usually wider than long, but 

 occasionally with the length and breadth nearly equal, greatest width at 

 or in front of the hinge-line, the cardinal. extremities rounded, rectangu- 

 lar, or more or less attenuate. The dimensions of a full grown example 

 are : length 20.5 mm., greatest width along the hinge-line 26.5 mm., thick- 

 ness 14.8 mm. The dimensions of another smaller and rounder example 

 are: length 15 mm., greatest width near the middle of the shell 17 mm., 

 length of hinge-line 13 mm., thickness 11.5 mm. 



Pedicle valve rather strongly convex, the greatest convexity posterior 

 to the middle, the beak pointed and incurved ; cardinal area concave, be- 

 coming more curved towards the beak, its height usually between 2 

 and 3 mm., the inferior portion sloping posteriorly at an angle of 

 about 135 degrees to the plane of the valve, the lateral margins sharply 

 defined and curving gently downward towards the cardinal extremities; 

 lateral slopes of the valve convex, except towards the cardinal extremi- 



