66 PALAEONTOLOGY OF KENTUCKY. 



davidsoni are only faintly developed, but covering the whole surface, while in 

 our specimen the ribs are well marked and limited to the central lobe. The 

 specimen from which the illustrations are made is the only one so far known 

 to me ; it is a well preserved, beautiful shell. 



Formation and Locality. I found it in the strippings of one of the quarries east of the city of 

 Louisville, in clay belonging to the Niagara group, and associated with other well known Upper Silurian 

 shells ; I feel, therefore, fully assured that it belongs to the Niagara fossils. 



Genus Chonetes. Fischer. 



Chonetes, Fischer. Oryckt. Moscow 1837. 

 Etymology : chone, a little cup. 



Shell semi -ova 1 or transversely oblong, with a wide straight hinge-line. Ex- 

 ternal margin of area of ventral valve furnished with a row of tubular spines. 

 Surface radiately striated, often spinose. Foramen in the ventral area distinct, 

 but partly closed by a pseudo-deltidium. Valves articulated by teeth and 

 sockets. Dorsal valve with a cardinal process, which is simple at the base, 

 but bifid or grooved at the extremity. Interior of the shell pustulose or papil- 

 lose. The genus Chonetes is nearly allied to Productus, from which it is dis- 

 tinguished by its articulated valves and row of tubular spines on the margin of 

 the ventral area, as well as by other characters of less importance. Unfortu- 

 nately the spines are often missing, having become obsolete by wear and rub- 

 bing. Even in the absence of these spines, Chonetes may be distinguished 

 from Producta by their less gibbous and ventricose ventral valve, and by their 

 finer surface striation. On the other hand, Chonetes, in form and external 

 appearance, makes an approach to the genera Strophomena and Leptaena, and 

 may be regarded as connecting link between the Sirophomenidae and Pro- 

 ductidae, 



Chonetes acutiradiata. HALL. 



Plate XVIII., figures 18, 19 and 20. 



Strophomena acutiradiata, Hall. Geol. Rep. 4th dist. N. Y. 1843. 

 Chonetes acutiradiata, Hall. Tenth Eep. on St. Cab., p. 117 1857. 

 Chonetes acutiradiata, Hall. Pal. N. Y., Vol. IV., p. 1201867. 



Shell of large size in its genus ; semi-circular ; sometimes more than twice as 

 wide as long ; the cardinal extremities produced and sometimes very mucro- 

 nate. Ventral valve moderately convex, sometimes a little gibbous in the 

 upper part, and frequently flattened or depressed at and below the middle; 

 greatest convexity a little above the middle, from whence it curves gently to 

 the front, somewhat abruptly depressed towards the cardinal extremities, 



