86 MISSISSIPPIAN BRACHIOPODA 



the costse the species resembles C. ornatus of the Louisiana limestone, but 

 the shell is more strongly convex with less well developed auriculations 

 and with less elevated costse. 

 Horizon. Kinderhook. 



CHONETES ORNATUS Shumard 

 Plate VIII, Figs. 21-29 



1855. Chonetes ornata Shumard, Geol. Rep. Mo., p. 202, pi. C, figs. la-c. 

 1894. Chonetes ornata Keyes, Mo. Geol. Survey, vol. 5, p. 53, pi. 38, fig. 2. 

 1899. Chonetes ornatus Girty, Mon. U. S. Geol. Survey, vol. 32, p. 527, 



pi. 68, figs. 4a-d. 

 1908. Chonetes ornatus Rowley, Mo. Bureau Geol. and Mines, vol. 8, 2nd 



ser., p. 75, pi. 17, figs. 20-23. 



Description. Shell subsemielliptical in outline, wider than long, the 

 length a little more than two-thirds the width, the greatest width usually 

 along the hinge-line, the cardinal extremities angular, the lateral margins 

 a little sinuate or nearly straight in the posterior half, passing with a 

 regular curvature into the anterior margin in front. The dimensions of 

 two examples are : length 6.9 mm. and 7.5 mm., width 10 mm and 11.5 mm., 

 convexity 2.7 mm. and 3 mm. 



Pedicle valve moderately convex, the greatest convexity near or a little 

 posterior to the middle, compressed towards the cardinal extremities with 

 a rounded ill-defined sinus passing from each side of the beak obliquely 

 to the lateral margins, the auriculations formed by these oblique sin- 

 uses are convex in an antero-posterior direction; mesial sinus obsolete or 

 represented by a slight mesial flattening of the valve ; beak small, com- 

 pressed, scarcely extending beyond the cardinal margin; cardinal area 

 narrow, nearly flat, extending posteriorly in nearly the plane of the 

 valve ; the delthyrium small, about as wide as high, about one-half of its 

 area, the apical portion, covered by a convex deltidium with a sinuate 

 cardinal margin; the cardinal margin sharply defined, sloping from each 

 side of the beak to the cardinal extremities and bearing one, two, or three 

 spines upon each side. 



Brachial valve rather deeply concave in the middle, flattened and auric- 

 ulate towards the cardinal extremities, the auriculations being concave in 

 an anterior-posterior direction ; cardinal area with a sharply defined 

 margin, much narrower than that of the opposite valve, the areas of the 

 two valves meeting in an obtuse angle ; at the center, opposite the delthy- 

 rium of the opposite valve,, a prominent, convex chilidium surrounds the 

 posterior surface of the cardinal process. 



Surface of each valve marked by from thirty to thirty-eight rounded 

 costae, none of which occupy the auricular portions, from two and one- 

 half to three occupying the space of one millimeter; those of the pedicle 

 valve increase by bifurcation and those of the brachial valve by implan- 



