PRODUCTUS 129 



Pedicle valve strongly convex, the umbonal region rather narrow and 

 conspicuously protuberant beyond the hinge-line, the surface curving 

 abruptly to the cardinal margin, compressed towards the cardinal ex- 

 tremities to form small but distinct auriculations, to the lateral and an- 

 terior margins the curvature is more gentle ; mesial sinus absent ; the 

 beak small, pointed and strongly incurved. Surface of the valve marked 

 by fine, regular, rounded costse, from two to three of which occupy the 

 space of one millimeter, all concentric markings inconspicuous or 

 wanting. 



Brachial valve not seen. 



Remarks. The specimens which, have been used for the basis of the 

 above description are Winchell's co-types from the upper yellow sand- 

 stone of the Kinderhook at Burlington, Iowa. The specimens are in the 

 condition of internal casts and do not preserve the markings of the pos- 

 terior portion of the shell. In the lower beds of the Burlington lime- 

 stone a small species of Productus occurs not infrequently, which is be- 

 lieved to represent this, same species, although it grows somewhat larger 

 than the types, often attaining a length of 12 mm. or more. These speci- 

 mens exhibit the surface markings better than the types, and the rounded 

 costse are seen to become nearly or quite obsolete before they reach the 

 apex of the beak, they increase by bifurcation at intervals and bear the 

 bases of spines which exhibit the tendency to be arranged in more or less 

 definite rows. Distinct concentric wrinkles are absent but more or less 

 regular lines of growth are present, in addition to which there are ex- 

 ceedingly fine concentric strire. The impressions of the brachial valve of 

 the Burlington specimens are similar in general form to the pedicle valve 

 except that they are much less convex, and the apical portion of the im- 

 pression is only slightly protuberant beyond the hinge-line. The essen- 

 tial characters of the species seem to be the small size, the absence of a 

 median sinus or fold, the small auriculations, and the nature of the sur- 

 face markings. 



Horizon. Upper Kinderhook and lower Burlington limestone. 



PRODUCTUS SAMPSONI "VVeller 

 Plate XIII, Figs. 30-35 



1909. Productus sampsoni "Weller, Bull. Geol. Soc. Am., vol. 20, p. 300, 

 pi. 12, figs. 18-22. 



Description. Shell small, usually longer than wide, regularly rounded 

 or somewhat pointed in front, the hinge-line shorter than the greatest 

 width, the cardinal extremities subangular or a little rounded. The di- 

 mensions of a nearly perfect specimen are : length from hinge-line to 

 front margin 8 mm., length from umbonal region of pedicle valve to front 



5 



