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PALAEONTOLOGY OF NEW YORK. 
Bilobites, Orthis, Dalmanella, Rhipidomella, Orthothetes, Anoplotheca, Lep- 
toccelia, Tropidoleptus. In the second group were placed species belonging to 
the genera Brachyprion, Strophodonta, Plectambonites, Lept^na, Productus, 
Chonetes, Stricklandinia ; in the third were Strophomena, Strophonella and 
Orthothetes. 
LIST OF GENERA AND SPECIES. 
The subdivisions here proposed for the genus Orthis, in its broader signifi¬ 
cance and usual acceptation, some of them under old names and others under 
new, are well founded in nature. This arrangement is the result of a careful 
study of a very extensive series of the American representatives of this genus, 
and of the nearly two hundred species which are currently referred to Orthis, 
a very large percentage will readily take their places in the proposed classifi¬ 
cation. It will be borne in mind that after the elimination of synonymous 
terms there still remain a considerable number of names, founded upon imper¬ 
fect or obscure material, which are of little aid to the student of palaeontology; 
others, upon fossils of great rarity or from horizons of uncertain age. In the 
following list of American species, which is appended in order to show the 
adaptability of this grouping, nearly all the members have been studied from 
actual specimens, the star preceding the names indicating this fact; the other 
species included being only those of which the original descriptions and figures 
have afforded some definite clue to their relation with these groups. 
