GENUS CENTRONELLA. 
399 
Genus CENTRONELLA (Billings, 1859). 
Recognizing the Genus Centronella as founded on C. glans-fagea, and 
taking the illustrations of the interior as given in the Sixteenth Report 
on the State Cabinet, p. 47, as the true representation of the loop, we feel 
warranted in uniting two or three other forms in the same generic rela¬ 
tion, from the general similarity of form, and compact shell substance, 
which is finely punctate. With our present knowledge, the genus begins 
its existence in the Schoharie grit, and is known in the Upper Helder- 
berg limestone and in the Hamilton and Chemung groups. It is not 
improbable that the genus may have a greater vertical range, and that if 
will be found among the terebratuloid forms of the Carboniferous period. 
The characteristic species, known in New-York, have the dorsal valve 
flattened or concave; but th e C.julia of Winchell has an oval form and 
convex dorsal valve, giving no indication, from these features, of its 
generic relations. 
Centronella glans-fagea. 
PLATE LXI. 
Rhynchonella glans-fagea : Hall. Tenth Report on the State Cabinet, p. 125. 1857. 
Centronella glans-fagea : Billings, Canadian Naturalist and Geologist, pp. 131 & 132. April 1859. 
« “ Hall, Sixteenth Report on the State Cabinet. 1863. 
( The species illustrated and discussed on pages 45, 46 and 47.) 
Shell small, broad-ovate or subquadrate; the sides often sloping from 
near the middle to the apex at an angle of about 85°; the front roun¬ 
ded ; the valves very unequal. 
Ventral valve much larger than the dorsal, very prominent, often sub- 
carinate along the middle and curving very abruptly to the lateral 
margins, regularly arcuate from beak to base. Beak much extended 
beyond that of the opposite valve, strongly incurved, bringing the 
apex above the plane of the margin of the dorsal valve. 
