496 MISSISSIPPIAN BRACHIOPODA 



determined. In its external characters the species most closely resembles 

 the Silurian Hindella umbonata (Bill.), from Anticosti, but that genus has 

 not been recognized outside of Anticosti and it is not likely that this 

 Kinderhook form is congeneric with that very much earlier species, es- 

 pecially in view of the fact that the genus has not been recognized any- 

 where in the intervening faunas. In one specimen observed, the posterior 

 portion of the shell is in the condition of an internal cast, and the median 

 portion of the brachial valve appears as a ridge running to a point under 

 the beak of the opposite valve, this condition being entirely similar to 

 that in the internal casts of undoubted athyroid shells, this ridge being 

 the cast of the canal which passes to the perforation through the hinge- 

 plate. The original reference of the species to the genus Spirigera was 

 essentially a reference to Athyris, but the contour of the shell is more nearly 

 like members of the genus Composita, except in the close approximation of 

 the beaks of the two valves, and the species is therefore placed in that genus. 

 Horizon. Chonopectus sandstone of the Kinderhook. 



