Wetter — Kinderhook Faunal Studies. 185 



Brachial valve deeply concave, abruptly curved and almost 

 geniculate in front ; cardinal extremities slightly contracted ; 

 upper half of shell marked by strong concentric wrinkles 

 and somewhat distant spiniform tubercles ; lower half of 

 shell marked by elongate spiniferous ridges." 



Remarks. This species was originally described from the 

 «* sandstone of the age of the Chemung group " at Burling- 

 ton, but it seems to be most abundant in the oolitic lime- 

 stone bed, all the specimens which have been studied being 

 from that horizon. When the original description was pub- 

 lished, the pedicle valve was said to be unknown, but an as- 

 sociated pedicle valve was described and illustrated as Pro- 

 dactus shumardianus . Clarksville, Missouri, and Burlington, 

 Iowa, were recorded as the localities for this latter species, 

 but the Burlington specimens should without doubt be in- 

 cluded in the P. concentricus. 



The pedicle valve is gibbous in the middle and compressed 

 at the cardinal extremities, it is flattened along the median 

 line, but with no sinus. The ornamentation is like that of 

 the brachial valve. An average sized specimen is 16 mm. in 

 length, 18 mm. in breadth, with the convexity of the pedicle 

 valve 9 mm. 



Some of the specimens which have been studied, and which 

 are evidently members of the same species, are marked by 

 much more numerous spine bases than those which have been 

 illustrated. 



The species was originally described as a member of the 

 genus Productus, but Schuchert has transferred it to Pro- 

 ductella. The essential features of the hinge which charac- 

 terize the genus Productella have not been observed in any 

 of the Burlington specimens, but in the character of its sur- 

 face ornamentation the species is more like members of the 

 genus Productella than like typical members of the genus 

 Productus. 



Productus arcuatus Hall. 



PI. XVI. f. 15. 



Original description. " Pedicle valve much elevated, longer 

 than wide, very gibbous, extremely arcuate, the beak recurved 



