PRODUCTUS 111 



Brachial valve gently concave throughout the visceral portion with 

 the* auriculations somewhat deflected, anteriorly and laterally the con- 

 cavity becomes greater as the curvature of the valve comes more nearly 

 in conformity with the margin of the other valve in its produced portion ; 

 the mesial portion of the valve sometimes slightly elevated in its anterior 

 half, in a low, obscure, mesial fold. Surface nearly free from radiating 

 markings towards the beak, but marked beyond this clear space by radiat- 

 ing series of elongated pits which are essentially discontinuous, radiating, 

 intercostal furrows ; rather strong, concentric, wrinkle-like markings cover 

 the visceral portion of the valve, and finer concentric lines of growth 

 cover the entire surface. 



Remarks. In the original definition of this species Miller referred to 

 two specimens which he illustrated as the types. One of these specimens, 

 the original of the first of the two illustrations, was correctly interpreted 

 as an external impression of the brachial valve, and this one is here se- 

 lected as the type of the species. The second specimen illustrated, and 

 interpreted as the internal cast of the pedicle valve, is really an external 

 impression of the brachial valve of quite a different species which is here 

 described as P. sedaliensis. Miller evidently did not have, and had not 

 seen the true pedicle valve of his species. P. blairi differs markedly from 

 other species of the genus in our Mississippian faunas in the marked in- 

 terruption of the radiating costge of the pedicle valve, giving the appear- 

 ance of series of elongate nodes, and in the interruption of the intercostal 

 furrows of the brachial valve, giving the appearance of series of elongated 

 pits. This style of ornamentation strongly suggests a relationship to some 

 of the Upper Devonian species which have been referred|to the genus 

 Productella, and it is possible that the species should be referred to that 

 genus, but since the presence or absence of hinge-teeth cannot be deter- 

 mined in any of the specimens examined, the species is allowed to re- 

 main in the genus Productus. 



Horizon. Chouteau limestone. 



' k 



PRODUCTUS INFLATUS McChesney 

 Plate X, Figs. 1-6 



1860. Productus inflatus McChesney, Desc. New Foss., p. 40. 



1865. Productus inflatus McChesney, 111. New Spec. Foss., pi. 6, figs. la-c. 



1868. Productus inflatus McChesney, Trans. Chicago Acad. Sci., vol. 1, 



p. 27, pi. 6, figs. la-c. 



Description. Shell of medium size or larger, usually longer than wide, 

 the greatest width along the hinge-line, the lateral margins a little sinuate, 

 in front of the cardinal extremities, rounding anteriorly into the anterior 

 margin which is a little sinuate in the middle. The dimensions of a rather 

 large pedicle valve which is broader than usual are : length from hinge- 

 line to anterior margin 20.9 mm., length from umbonal region to anterior 



