CHONETES 87 



tation. In addition to the costae each valve is ornamented by exceedingly 

 fine concentric markings, stronger on the pedicle than on the brachial 

 valve, which are obsolete in the furrows between the costae, and by 

 stronger concentric lines of growth which sometimes become lamellose. 



Remarks. This species has sometimes been confused with the form here 

 referred to C. glenparkensis, indeed Shumard, the author of the species, 

 probably included in it specimens which are really C. glenparkensis, as he 

 mentions a Chouteau limestone locality, Cooper County, Missouri, as one 

 of his type localities. Among recent collections the species has been ob- 

 served only in the fauna of the Louisiana limestone, all the Chouteau lime- 

 stone examples with similar markings being C. glenparkensis. The species 

 differs from C. logani in its somewhat larger size, its more conspicuous 

 auriculations, its stronger and somewhat coarser costae. It resembles 

 C. logani in its fine concentric markings which are conspicuous upon the 

 tops of the costae and become obsolete in the intervening furrows. 



Horizon. Louisiana limestone. 



CHONETES GLENPARKENSIS "Weller 

 Plate VIII, Figs. 30, 47-49 



1906. Chonetes glenparkensis "Weller, Trans. St. Louis Acad. Sci., vol. 16, 

 p. 441, pi. 6, fig. 7. 



Description. Shell subsemielliptical in outline, the length about two- 

 thirds the width, the greatest width along the hinge-line, the cardinal ex- 

 tremities acutely angular and sometimes a little acuminate. Lateral 

 margins nearly straight or slightly concave posteriorly, their directions 

 converging anteriorly, towards the front they round into the regularly 

 convex anterior margin without interruption. The dimensions of two 

 specimens are: length 8 mm. and 7.5 mm., width 12.5 mm. and 12.4 

 mm., convexity 2.8 mm. and 3 mm. 



Pedicle valve strongly convex, inflated in the central portion and con- 

 spicuously compressed towards the cardinal extremities, the auriculations 

 convex from the cardinal margin anteriorly, the greatest convexity of the 

 valve near the middle, the surface curving a little more abruptly to the 

 beak than to the anterior margin ; mesial sinus obsolete ; the umbo rather 

 prominent and a little protuberant beyond the cardinal margin; the 

 beak small and incurved ; cardinal margin sharply defined, with three or 

 four spines on each side of the beak directed obliquely outward. Inter- 

 nally the muscular scars are only moderately developed, being divided 

 along the median line of the shell by a slight ridge extending anteriorly 

 from the beak ; beyond the region occupied by the muscular impressions 

 the surface is strongly papillose, the papilla? being arranged in more or 

 less regular, radiating lines and being obsolete towards the cardinal ex- 

 tremities. 



