86 THE DEVONIAN OF MISSOURI. 



the University of Missouri if 40 mm. wide, 28 mm. long, with a convexity of the pedicle 

 valve of 13 mm. 



Pedicle valve strongly convex in small specimens, moderately convex in large, great- 

 est convexity posterior to the middle; the umbonal region projecting considerably 

 beyond the hingeline; cardinal extremities well differentiated in large specimens, not 

 differentiated in small; no mesial sinus; beak small and strongly incurved. 



Brachial valve moderately concave, with the surface slighly deflected towards the 

 cardinal extremities. The cardinal process is small, bifid, each division excavated longi- 

 tudinally on its outer surface. From the base of the cardinal process a pair of shallow 

 furrows extends outward at an angle of about 80° from the median line of the shell 

 to near the cardinal extremities and back of the furrow a low ridge forms its boundary. 

 From the base of the cardinal process an illdefined furrow runs forward for about one- 

 fourth the length of the shell, where it is replaced by a sharp-topped narrow low median 

 septum which extends about one-third the length of the shell. The brachial impressions 

 are weak and extend about three-fourths the width and length of the shell. The inner 

 surface is covered by radiating papillae. 



Surface of both valves marked by a few lines of growth. Spines slender, numerous, 

 arranged in irregularly concentric and radiating lines. A specimen 19 mm. wide has 

 one spine 1/8 mm. in diameter and 2^ mm. long preserved. The spines are recumbent 

 and often against the shell for one or two millimeters. The brachial valve spines are not 

 infrequently missing, but all well preserved specimens have them. 



Remarks — This species differs from P. subalata Hall of the Cedar Valley limestone 

 in the abundance of spines, slenderness of spines, recumbency of spines, much less con- 

 vexity, and greater comparative width of large specimens. Rowley's P. marquessi 

 seems to belong with Swallow's species. The absence of spines on the brachial valve 

 would be sufficient to differentiate it, but many of the specimens of P. callawayensis 

 Swallow show only very faint spines owing to poor preservation. This is shown in 

 figure 13 of plate 15. 



Occurrence — Snyder Creek shale of Callaway County. 



Productella spimdicosta Hall 



1854. Productus subaculeatus Norwood and Pratten (non Murchison), Jour. Acad. 



Nat. Sci., Philadelphia, III, p. 21. 

 1857. Productus spinulicostac Hall, Tenth Rep. N. Y. State Cab. Nat. Hist., p. 173. 

 1867. Productella spinulciosta Hall, Pal. New York, IV., pt. I, p. 160, pi. 23, figs. 6-8, 



25-34. 

 1897. Productella spimdicosta Schuchert. U. S. Geol. Surv., 87, p 318. 

 1901. Productella spinulicosta Kindle, Indiana Dept. Geol. Nat Res., 25th Ann. Rept., 



pp. 629-630, pi. 6, figs. 9 and 9a. 

 1903. Productella spinulicosta Clarke, N. Y. State Mus., Bull. 65, p. 292. 

 1909. Productella spinulicosta Grabau and Shimer, North American Index Fossils, I, 



p. 241, figs. 293c, d. 

 1913. Productella cf. spinulicosta Prosser and Kindle, Maryland Geol. Survey, Middle 



and Upper Devonian, ppl. 162-163, pi. 13, figs. 17-20. 

 Hall's description — "Ventral valve gibbous, length and breadth about as seven to 

 eight; hinge extremities angulated, and the margins being contracted a little below 

 form small ears, while below this contraction the sides are regularly curved and the 

 front is broadly rounded. The umbo is considerably elevated above the hinge line and 

 the apex incurved. Surface marked by closely arranged concentric striae and studded 

 with slender rounded spines. On the upper part of the shell and on the ears these spines 

 are round at the base, and rise directly from the surface. On the middle and lower part 

 of the valve there is a slight elevation of the surface a little above the base of the spine, 



