316 MISSISSIPPIAN BRACHIOPODA 



is a constant one. The younger individuals of S. marionensis possess 

 similar mucronate cardinal extremities, but the hinge-line does not con- 

 tinue to increase in length through the entire life of the individual as 

 it does in 8. osagensis. 



The shell illustrated by Meek from the Ohio Waverly as S. biplicatus 1 

 resembles this one very closely in general form and size and may be 

 identical, it is certainly entirely different from the true 8. biplicatus, \Yell 

 preserved examples of this shell from Licking County, Ohio, preserve the 

 minute, surface characters perfectly, which consist of fine, exceedingly 

 regular, concentric marks, which are crossed by still finer radiating striae, 

 giving the surface a very beautiful reticulate appearance. None of the 

 Missouri examples of 8. osagensis are preserved so as to show such mark- 

 ings, but if they should be present the identity of the Ohio shells is more 

 sure. 



Horizon. Kinderhook. 



SPIRIFER LATIOR Swallow 

 Plate XXXVIII, Figs. 9-13 

 1863. Spirifer latior Swallow, Trans. St. Louis Acad. Sci., vol. 2, p. 86. 



Description. Shell small, subsemicircular in outline, the greatest width 

 along the hinge-line, the cardinal extremities angular. The dimensions of 

 a nearly perfect specimen are: length of pedicle valve 12.5 mm., length 

 of brachial valve 10 mm., width along hinge-line 15.5 mm., thickness 9 

 mm., height of cardinal area 2.5 mm. 



Pedicle valve rather strongly convex with the greatest convexity 

 posterior to the middle and well towards the umbo, the surface curving 

 abruptly to the cardinal margin, the slopes from the umbo to the 

 cardinal extremities at first gently convex, becoming a little concave 

 towards the cardinal extremities, to the anterior and antero-lateral 

 margins the curvature is gently convex; beak small, pointed and in- 

 curved; cardinal area of moderate height, concave, the lateral margins 

 sharply defined and sloping from the sides of the beak to the cardinal 

 extremities; mesial sinus originating at the beak as a narrow, sharply 

 defined groove-like depression becoming broader and ill-defined anter- 

 iorly where it is rather shallow and rounded in the bottom, a rounded 

 median plication originates in the umbonal region and continues to the 

 front without subdivision, upon each side of the median one there is a 

 single similar plication which originates from the inner margin of the 

 bounding plications of the sinus; each lateral slope of the valve marked 

 by 12 to 15 simple, rounded plications which decrease regularly in size 

 towards the cardinal extremities. 



I Spirifer biplicatus ? Meek, Pal. Ohio, vol. 2, p. 290, pi. 14, fig. 5 (1875). 



