366 MISSISSIPPIAN BRACHIOPODA 



are similar in size and proportions and possess the same form of minute 

 radial corrugations, but the more minute concentric markings have been 

 almost obliterated in all specimens examined. The mesial sinus in the 

 pedicle valve of the Chouteau limestone examples is perhaps slightly 

 more angular than in the Ohio specimens, but without more evidence 

 this character is not of enough importance to justify a specific differ- 

 entiation. 

 Horizon. Waverly group and Chouteau limestone of the Kinderhook 



SPIRIFER MORTONANUS Miller 

 Plate LVIII, Figs. 1-3 ; Plate LIX, Figs. 1-6 



1870. Spirifer fastigatus Meek and Worthen, Proc. Acad. Nat. Sci. Phil., 



p. 36. (Not S. fastigatus Morton, 1836.) 

 1875. Spirifer fastigatus Meek and Worthen, Geol. Surv. 111., vol. 6, p. 521, 



pi. 30, fig. 3. 



1883. Spirifera mortonana Miller, Am. Pal. Foss., 2nd ed., p. 298. 

 1895. Spirifer Mortonanus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 38, 



figs. 18, 19. 



Description. Shell above medium size, much wider than long, the greatest 

 width along the hinge-line, the cardinal extremities acutely angular. The 

 dimensions of two individuals are : length 39 mm. and 34 mm., width 69 

 mm. and 63 mm., thickness 35 mm. and 27.5 mm., height of cardinal area 

 8 mm. and 6 mm. The width of the largest specimen observed is 96 mm. 



Pedicle valve convex in the middle on each side of the sinus, the curva- 

 ture usually becoming a little more abrupt as it approaches the antero- 

 lateral margins, the surface becoming compressed or concave towards 

 the cardinal extremities, often developing a more or less distinct oblique 

 sinus on each side passing from near the beak to the lateral margins 

 just in front of the cardinal extremities, the umbonal region rather broad ; 

 beak small and pointed, incurved; cardinal area rather high, arched, 

 the curvature increasing towards the beak, the inferior portion sloping 

 posteriorly at an angle of about 120 degrees to the plane of the valve, 

 the lateral margins sharply defined, extending laterally from the beak 

 with a very slight slope, being sub-parallel with the cardinal margin 

 nearly to the end, where they drop off abruptly to the cardinal extrem- 

 ities ; delthyrium large, wider than high, the surface of the area vertically 

 striate and marked by faint, longitudinal lines of growth; lateral slopes 

 of the valve each marked by from 10 to 12 rounded or subangular plica- 

 tions near the beak which grow gradually smaller towards the cardinal 

 extremities, beyond them a considerable area of the shell is marked by 

 much finer plications, 6 or 8 of which can be detected in some individuals, 

 while in others they are nearly obsolete, from 2 to 6 of the larger plica- 

 tions on each lateral slope divide in the umbonal region and continue 



