256 TRANSACTIONS OF THE [MAR. 15, 



3 is drawn from a wax impression of one of the most prominent 

 and most deeply bifid specimens; it ranges from this form to a 

 comparatively low process with the bifurcation almost obsolete. 

 The species is named in honor of Prof. H. S. Williams. 



Productus cestriensis Worthen.* 

 PI. XIX., figs. 7-9. 



1855. Productus elegans, Norwood and Pratten, Jour. Acad. Nat. 



Sci. Phil. (2), Vol. 3, p. 13, PI. 1, figs. 7a-c. (Name pre- 



occupied.) 

 1860. ProduQtus cestriensis, Worthen, Trans. St. Louis Acad. 



Sci., Vol. 1, p. 570. 

 1891. Productus elegans, Whitfield, Ann. N. Y. Acad. Sci., Vol. 



5, p. 581, PI. 13, figs. 15-16. 

 1895. Productus elegans, Whitfield, Geol. Surv. Ohio, Vol. 7, p. 



669, PL 9, figs. 15-16. 

 Shell of medium size, subelliptical in outline, hinge line 

 straight, very short. 



Pedicle valve strongly arcuate, much broader towards the 

 front than along the hinge-line, with almost no auricular depres- 

 sions at the extremity of the cardinal line. Beak rather large 

 and obtuse. A shallow, ill-defined mesial sinus extends from 

 near the beak to the anterior margin. Surface ornamented with 

 from thirty to fifty, fine, longitudinal, bifurcating plications 

 which often become fasciculated towards the anterior margin, 

 giving that portion of the shell a wrinkled appearance. In the 

 older shells the pedicle valve is often broadly and rather abruptly 

 expanded towards the margin. 



Brachial valve flattened throughout the greater part of its 

 surface, but abruptly bending upward near the margin. 



Though this species is exceedingly variable in many respects, 

 it possesses some remarkably constant characters. The most 

 noticeable of these is the shortness of the hinge-line as compared 

 with the width of the shell towards the front, with the obsolete 

 or nearly obsolete auriculations at its extremities. The striking 

 quadrangular appearance of the shell when viewed posteriorly 

 is also a noticeable characteristic, though not so pronounced in 

 the Batesville specimens as in those from some other localities. 

 The specimen illustrated in the accompanying figures shows this 

 characteristic much less than do many others, due to the more 

 rapid expansion of the shell towards the front, 



* A complete list of references to the species here described is not always given. In 

 a Bibliographic Index of American Carboniferous Invertebrates, now in preparation 

 by the author, a complete list of references with geographic distribution will be given 

 of all American Carboniferous invertebrates. 



