220 PALEONTOLOGY 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 Steophomena, 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. 



