PLATE IV. 
ZAPHRENTIS FENESTRATA, Nich. Nat. size. (p. 22.) 
BLOTHROPHYLLUM APPROXIMATUM, Nich. Nat size. (p. 19.) The epitheca has 
been decorticated. 
BLOTHROPHYLLUM DECoRTICATUM, Billings. A fragment from which the epitheca 
has been removed. Nat. size. (p. 19.) 
CLISIOPHYLLUM ONEIDAENSE, Billings. A small example from which the 
epitheca has been removed. Nat. size. (p. 20.) 
Another specimen of the same, in which the epitheca is also wanting, 
