REVISION OP THE GENUS ORTHIS. 



19 



Professor James Hall then presented two oral communications, the sub- 

 stance of which is contained in the following abstracts : 



SOME SUGGESTIONS REGARDING THE SUB-DIVISION AND GROUPING OF 

 THE SPECIES USUALLY INCLUDED UNDER THE GENERIC TERM ORTHIS, 

 IN ACCORDANCE WITH EXTERNAL AND INTERNAL CHARACTERS AND 

 MICROSCOPIC SHELL STRUCTURE. 



BY JAMES HALL. 



* 



[Abstract."] 



The writer is aware that several generic names have already been proposed for 

 species usually arranged under the designation of Orthis. Recent investigators have 

 found it necessary to make farther sub-division, and to propose new generic terms. 



The following grouping of the species has been adopted by the writer for a long 

 time, but no publication has been made. The seventy-four species which have been 

 especially studied seem to be very naturally arranged under the sub-divisions pro- 

 posed, and are submitted to the American Geological Society with the desire to elicit 

 information and legitimate criticism. 



Unfortunately the writer has not had access to the latest publications on the Brach- 

 iopoda which have appeared in Europe, and therefore he does not know how far 

 Prof. (Ehlert and others may have anticipated the suggestions embodied in this 

 paper. 



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Pro-posed sub-division of the genus Orthis. 



group, (shell im punctate) Low. Cambrian — Clinton. 



" ( " ) Chazy — Clinton. 



" ( " ) Chazy — Niagara. 



" ( " ) Chazy — Niagara. 



" (shell punctate) Chazy— Corniferous. 



" ( " ) Niagara — Up. Carb. 



O. propinqua (Schizophoria) group, (shell punctate) Clinton— Carboniferous. 

 0. (Bilobites) (Dicoelosia) biloba group, (shell punctate) Niagara— L. Held. 



O. occidentalis 

 O. (Platystrophia) 

 O. plicatella 

 0. tricenaria 

 O. testudinaria 

 O. hybrida 



Species which have been studied and placed under the proposed grouping 

 « to be studied and placed under the proposed grouping 



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