Maryland Geological Survey " 337 



CnoNETES HUDSOxicus Clarke 

 Date LXI, Fig. 15 



Chonetcs hudsonica Clarke, 1900, Mem. N. Y. State Mus., vol. ill. No. 3, p. 49, 



pi. vli, figs. 1-6. 

 Chonetes hudsonica Weller, 1903, Geol. Surv. N. J., Pal., vol. Hi, p. 347, pi. 



xlvi, fig. 11. 



Description. — " This is tlie only normally convex Chonetes found in 

 this fauna. The shell is of medium or small size, transverse in outline; 

 hinge-line marking the greatest width of the shell; lateral margins sub- 

 parallel for a short distance and rounding rather abruptly to a nearly 

 transverse anterior margin. Surface of the pedicle valve quite unifonnly 

 convex, with a faint median sinus seen only over the anterior portion of 

 the valve. The surface strije are fine, round and close together, with very 

 narrow interspaces. They increase rapidly and irregularly by bifurcation 

 and implantation. Yeiy fine, concentric lines are sometimes visible with 

 favorable preservation. The cardinal spines are two or three in number 

 on each side of the beak and are directed outward. 



" On the brachial valve a fold to correspond to the obscure median sinus 

 of the pedicle valve is not always to be seen. So far as observed, the multi- 

 plication of the strife of this valve seems to be wholly by bifurcation. 

 With respect to their interior characters, both valves present normal 

 structure with a considerable development of the median septum in the 

 pedicle valve." Clarke, 1900. 



Before Clarke described this species the writer identified it with C. 

 melonica Billings. As the former points out, however, that species has a 

 slightly different outline and a greater number of striae. In C. liudsoniaus 

 there are about twenty stria? in 5 mm. and in C. melonica about twenty^ 

 five in the same space. Clarke's specimens also seem to be smaller than 

 Billings's species, but the writer has an example from Becraft Mountain 

 17 mm. in width; at Camden, Tennessee, it reached 21 mm. in width, and 

 about Cumberland, 24 mm. In New York the species has from two to 

 three cardinal spines on each side of the beak and in the southern material 

 there are usually three. 



Length 12 mm. ; width 23 mm. 

 22 



