312 PALEONTOLOGY OF NEW YORK. 



Genus CHONOPECTUS, gen. nov. 



PLATE XVu, FIGS. 20-23; and PLATE XVI, FIGS. 17, 31. 



1854. Chonetes, Norwood iiiid Pratten. Journal Acad. Nat. Sci. Phila., vol. ii, p. 25. 

 1858. Chonetes, Hall. Geological Survey of Iowa, vol. i, jjt. ii, p. 517, pi. vii, fig. 1. 

 1883. ClioTietes, Hall. Second Ann. Rept. N. Y. State Geologist, pi. xvii, fig. 17. 



This name is proposed for the species, Chonetes Fischeri, Norwood and 

 Pratten, a large, normally concavo-convex shell, with a sub-semicircular 

 outline ; occurring in the oolitic limestone and yellow sandstone of the Burling- 

 ton beds of Iowa. In this species the cardinal margin of the pedicle-valve 

 bears a row of erect spines, as in Chonetes. The beak is often compressed 

 or distorted in such a manner as to leave a flattened area, which resembles, 

 and probably is a cicatrix from attachment in early growth. This charac- 

 ter is more prominent in some individuals than in others, and appears to have 

 become consideraby obscured by the later growth of the shell. The surface 

 ornamentation is also peculiar ; the shell bearing a double oblique series of 

 concentric lines, which give to the surface the appearance of the engraving on 

 a machine-turned watch case. These lines are wrinkles rather than striae, and 

 are strongest over the umbonal and central region, where traces of them may 

 sometimes be observed on internal casts of the valves. The wrinkles are 

 crossed by a normal series of very fine concentric growth-lines, and beneath 

 these, but not always exposed, are exceedingly fine, crowded, radiating strise, 

 usually very much interrupted in their course from beak to margin, and often 

 flexuous and irregular. Sometimes the surface is entirely free from the double 

 series of concentric wrinkles, and marked only by the fine radiating and con- 

 centric striae. 



The internal muscular impressions of the species have not been fully deter- 

 mined. Casts of the pedicle-valve show the impression of a short median 

 septum dividing two broad obcordate flabelliform muscular scars, from the outer 

 margin of which sometimes originates a series of irregularly radiating furrows 

 or ridges, which were probably of vascular origin. Impressions of a very nar- 

 row cardinal area and exceedingly small hinge-teeth are also seen on internal 

 casts of this valve. 



