CHONETES 91 



mine whether his statement in regard to the size of the costae is correct, 

 but these shells from the "Button Mould Knobs" cannot be referred to 

 any other described species, and if they are not C. shumardanus they must 

 belong to an unnamed form. 



This shell has sometimes been confused with C. illinoisensis, with which 

 some specimens agree closely in form, size, and size of costse, but they con- 

 stantly differ from that species by reason of the transverse markings or 

 crenulations of the costas which are entirely absent in C. illinoisensis. 

 As regards these markings of the shell, C. shumardanus resembles C. 

 logani and C. ornatus, but it differs from both these species in other essen- 

 tial characters. 



Horizon. New Providence shale of the Kinderhook, Kentucky. 



CHONETES GBEGARIUS Weller 

 Plate VIII, Figs. 71-72 



1901. Chonetes gregarius Weller, Trans. St. Louis Acad. Sci., vol. 11, 

 p. 149, pi. 12, fig. 2. 



Description. Shell small, usually subelliptical in outline, the length 

 about four-fifths the width, hinge-line usually a little shorter than the 

 greatest width of the shell and the cardinal extremities a little rounded, 

 but in some specimens the cardinal extremities are rectangular and the 

 hinge-line equal to the greatest width of the shell. Lateral margins 

 gently convex or sometimes nearly straight posteriorly, becoming more 

 convex anteriorly and rounding without interruption into the anterior 

 margin, which is gently convex in its median portion. The dimensions 

 of three specimens are : length 4.2 mm., 5.1 mm., and 6.1 mm. ; width 5.8 

 mm., 6 mm., and 8 mm. ; convexity 1.5 mm., 1.6 mm., and 2 mm. 



Pedicle valve most convex at a point posterior to the middle, from 

 which point the surface curves more abruptly to the beak than to the 

 front margin, the convexity of the valve often extends well out towards 

 the cardinal extremities, the amount of compression of the valve in 

 that region being variable but never excessive; mesial sinus obsolete; 

 the beak small, scarcely extended beyond the cardinal margin; car- 

 dinal margin sharply defined, bearing the bases of about two spines 

 on each side of the beak ; cardinal area narrow, lying in nearly the plane 

 of the valve, the delthyrium of medium size, closed at its apex by a 

 convex deltidium. Internally a slight median ridge extends anteriorly 

 from the beak, the muscular scars are weakly developed and the sur- 

 face is papillose towards the anterior and lateral margins. 



Brachial valve moderately concave, the greatest concavity posterior 

 to the middle, the surface flattened towards the cardinal extremities; 



