BLACK RIVER BRACHIOPODS 
77 
excessive gibbosity and very slight development of fold and sinus. 
In the young specimens there is a lesser development of these 
features, coupled with a flattening or concavity near the cardinal 
extremities, that indicate close relationship to, and perhaps descent 
from Z. variabilis. It seems probable that both recuruirostris and 
calhounensis are the descendants of a species very much like Z. 
variabilis. 
Cotypes, No. 27,457, Paratypes, No. 27,458, Walker Museum. 
