and allied Brachiopod genera. 403 
nearly to the front, and is reflected, but the laminw are not 
united until after they are folded back.” 
In Centronella, as thus illustrated, we have a simple loop, or 
the two limbs becoming united at an acute angle at the point of 
greatest anterior extension, whence they recurve in a thin verti- 
cal plate which is not attached at either margin; approaching, 
in some respects, to Waldheimia. 
This internal feature is accompanied, in the cast of C. Glans- 
fagea, the typical form of the genus, by other differences which 
distinguish it from the casts of typical species of Crypionella. 
6. 
16. 1 1% 
= 
Fig. 15. Ventral view of cast of Centronella Glans-fagea.—Fig. 16. Dorsal view 
of cast of the same.—Fig. 17. Profile view of the same. 
In the cast of a ventral valve of C. Glans-fagea, fig. 15, we 
_ The interior of the ventral valve of Centronella impressa* shows 
Similar strong rounded and blunt dental lamellx, with a deep 
_ Tostral cavity and muscular markings, which would give a cast 
Similar to that of C. Glans-fagea. 
The cast of the dorsal valve of C. Glans-fagea presents a 
slightly concave surface, and on each side of the apex two large 
and deep cavities made by the bases of the crural processes ; 
and between them is a narrow filling of stone. The centre is 
Mar i 
crura, are some points marked as if for muscular attachment 
(see b, fig. 16). 
* A very distinct species from C. Hecate (Billings) of the Oriskany Sandstone, 
which differs mainly in size from Cnctseaelte lthyohonaiia ?) alveata (Hall), Tenth 
Report on the State Cabinet, 1857. 
