312 
PALAEONTOLOGY OF NEW YORK. 
Genus CHONOPECTUS, gen. nov. 
PLATE XVb, FIGS. 20-23; AND PLATE XVI, FIGS. 17, 31. 
1854. Chonetes, Norwood and Pratten. Journal Acad. Nat. Sci. Phila., vol. ii, p. 25. 
1858. Chonetes, Hall. Geological Survey of Iowa, vol. i, pt. ii, p. 517, pi. vii, fig. 1. 
1883. Chonetes, Hall. Second Ann. Kept. 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 striae, 
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. 
