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PALAEONTOLOGY OP NEW-YORK. 
Spirifera duplicata. 
Delthyris duplicata : Conrad, Jour. Acad. Nat. Sciences Philadelphia, Vol. viii,-pa. 261, pi. 14, f. 16. 
“ “ ; Id. Ib., referred to under S. granulifera. page 223 of this volume. 
Since the preceding pages were sent to the press, I have observed, among some 
specimens from the coarser shales of the Hamilton group, the cast of a Spirifer 
with duplicate mesial fold and angulated ribs, corresponding to the original de¬ 
scription of S. duplicata. The material at hand is not sufficient to determine its 
specific value. 
Spirifera carticosa. 
Spirifer corticosa : Hall, Tenth Report on the State Cabinet, p. 160. 1857. 
Of this species, I have not obtained sufficient material to satisfy me of its claim 
to specific distinction. A well-marked ventral valve, which I have referred to this 
species, still remains unidentified with any other species; while two other well- 
marked individuals*, originally referred to the same, prove to be quite distinct 
from this and every other species;, so that in the present state of knowledge, I 
propose to leave the specimens'without illustration, and subject to future revision. 
Spirifera tenuis. 
Spirifer tenuis : Hall, Tenth Report on the State Cabinet, p. 162. 1857. 
The specimens on which this species was originally founded are silicified in whole 
or in part, and it is impossible to know satisfactorily what effect the silicification 
and partial solution of the shell may have had in removing or modifying surface 
characters. This species is therefore left undetermined for the present. 
Spirifera pertenuis. 
Spirifer pertenuis : Hall, Tenth Report on the State Cabinet, p. 163. 1857. 
The specimens of this species are in a condition similar to the last, and are 
consequently left for farther study. 
These are probably not from the Hamilton group, though given to me as authentic. 
