GEOLOGY OF THE FOURTH DISTRICT. 



ORGANIC REMAINS OF THE HAMILTON GROUP. 



No. 45. — No. 84, page 205. 

 Fig. 1. Dipleura Dekayi (head), Green (Monograph, p. 79). 

 Fig. 2. Orthonota undulata, Conrad (Annual Geol. Reports). 

 Fig. 3. Delthyris mucronata, Conrad (Annual Reports). This is the common form of this 



fossil in the sandy shale of Eastern and Central New-York ; at the west it is less 



elongated and more rotund. See figs. 2 and 3 of No. 41. 



No. 46. — No. 8G, page 208. 

 Figs. 8, 8 a and 8 b. Delthyris medialis, H. Moscow. 



Figs. 9 and 9 a. Two views of a young shell of the same species as the above. Moscow 

 Fig. 10. Delthyris fimbriata, Conrad (Jour. Acad. Nat. Sci. Vol. 8, p. 263). 

 Fig. 10 a. Cast of the upper valve of the same fossil. 

 Fig. 10 b. A small portion of the shell magnified. Moscow. 



