Weller — Kinderhook Faunal Studies, 71 



Productus COOPERENSI8 Swall.? 



PL I.f. 3-4. 



The specimens in the University of Michigan collection, 

 referred by Winch ell to this species, differ from P. semire- 

 ticulatus chiefly in the nearly obsolete radiating plications. 

 The specimens are also more gibbous than those that are more 

 completely plicated. Associated with these specimens there 

 are others which are intermediate in their characters between 

 the two forms, and it is not improbable that both those re- 

 ferred to P. cooperensis and to P. semireticulatus are mem- 

 bers of a single variable species. The original P. cooperensis 

 was described from the Chouteau limestone of Cooper County, 

 Missouri. It has never been illustrated and the identity of 

 these Burlington specimens with it is by no means certain. 



Productus laevicostus White. 



PL I, f. 1-2. 



This species, first described from the Burlington limestone 

 at Burlington, Iowa, is a member of the group of species of 

 Productus typified by P. cora. All the species of this group 

 are characterized by their fine, dividing, more or less wavy, 

 radiating costae, and by the conspicuous transverse wrinkles 

 of the shell in the region of the cardinal extremities, P. lae- 

 vicostus is closely related to the typical P. cora as it occurs 

 in the Coal Measure faunas, but the beak is always much more 

 pointed than in the latter species, and it is also more free from 

 spines. 



Productella nummularis (Win.). 



PL I.f. 9-10. 



Strophalosia nummularis, Bull. U. S. G. S. 153: 613. 



Shell subcircular in outline, truncated by the hinge-line; 

 hinge-line shorter than the greatest width of the shell. Pedi- 

 cle valve depressed convex, most prominent at a point a little 

 in front of the beak, decidedly flattened on each side of the beak 

 towards the cardinal extremities ; the beak, rather small and 

 pointed, incurved, projecting but slightly beyond the hinge- 

 line. Brachial valve discoid, with a broad, shallow mesial 

 depression which is bounded on the two sides by lines diverg- 

 ing from the beak nearly at right angles to each other ; beak 



