GENUS CENTRONELLA. 399 



CiEBTUS CexTROXELLA (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 i§ 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 it 

 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 the C.julia of Winchell has an oval form and 

 convex dorsal valve, giving no indication, from these features, of its 

 generic relations. 



Centronella glans-fa^ea. 



PLATE LXI. 



Rhynchonella glant-fagea : Hall. Tenth Report on the State Cabinet, p. 125. 1867. 

 Centronella glam-fagea : Billinos, Canadian Naturalist and Geologist, pp. 131 & 132. April 1859. 

 *• " Hall, Sixteenth Report on the State Cabinet. 1863. 



( The iprcies 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. 



