86 University Geological Survey of Kansas. 



Measurements: Length, 26mm.; width, 30mm.; convex- 

 ity, 16 mm. 



Range and distribution : Upper Coal Measures ; Kansas City, 

 Turner, Eudora, Lawrence, Lecompton, Topeka, Manhattan, 

 and Grand Summit. Common throughout the Upper Coal 

 Measures of the state. 



This shell, when found with the shell and spines well pre- 

 served, looks so very different from specimens which are ordi- 

 narily found with the spines removed that one could hardly 

 imagine that they were the same. Those without the spines 

 seem to be complete specimens, with regular, concentric zones 

 of elongated tubercles, betraying very little indication that they 

 are the bases of detached spines. 



This shell is very readily distinguished from the foregoing 

 species by its narrow, prominent beak and its peculiar surface 

 markings. The concentric zones of spines are found on none 

 of them. 



Productus symmetricus. Plate IX, figs. 6-6b. 



Productus symmetricus McChesney, New Pal. Foss., p. 35. (1860); Trans. 

 Chic. Acad. Sci., i, p. 25, pi. i, f. 9, (1868); Meek, Fin. Rep. U. S. 

 Geol. Surv. Neb., p. 167, pi. v, f. 6, pi. vin, f. 13, (1872); etc. 



Meek*s description (in part) : " Shell of medium size, sub- 

 orbicular, or a little wider than long ; hinge line somewhat less 

 than the greatest breadth ; sides rounding regularly to the 

 front, which is rather broadly rounded in outline ; ventral 

 valve somewhat compressed, or only moderately convex, with- 

 out any traces of a mesial sinus ; ears compressed but not 

 abruptly separated from the swell of the umbo, obtusely an- 

 gular or a little rounded at the extremities ; beak moderately 

 large, incurved, but not curving much within the hinge margin. 

 Dorsal valve rather evenly, and only moderately concave, car- 

 dinal process slender, prominent, curved [not always] , trifid, 

 the middle division being more prominent than the others, and 

 emarginate at its extremity, the emargination being caused by 

 a distinct mesial furrow that extends the entire length of the 

 process [and sometimes two-thirds the length of the mesial 

 septum] ." Lateral ridges elevated, extending outward parallel 



