350 E. M. KINDLE 



Atrypa spinosa c 



Stropheodonta (Douvillana) mucronatus a 



Stropheodonta perplana var. nervosa r 



Schizophoria tioga c 



Rhipidomella sp r 



Camarotoechia sp r 



Spirifer disjunctus c 



Edmondia sp r 



Schizodus rhombeus r 



Sphenotus contractus c 



Loxonema sp r 



The case of recurrence which has been cited involves a somewhat 

 different phase of the phenomenon from that represented in the 

 New York occurrences of T. carinatus in the Chemung. 



The presence of a recurrent Hamilton species like Tropidolep- 

 tus carinatus in the Chemung fauna of southern New York involves 

 its withdrawal from at least the major part of the New York area 

 at the end of Hamilton sedimentation to some part of the sea 

 furnishing a more congenial environment than that which accom- 

 panied Genesee and Portage sedimentation. In the newly 

 adopted habitat or in a small portion of the old one it found a 

 haven where those conditions of the Hamilton sea which were 

 essential to its life were maintained throughout Genesee and 

 Portage time. With the initiation of Chemung sedimentation 

 T. carinatus extended its habitat back again over a part of the 

 area which it had previously occupied. 



The case of recurrence which I have given in Virginia does not 

 involve, as in New York, a retreat of the species before unfavorable 

 conditions at the close of the Hamilton and later recovery of lost 

 territory, since it apparently never occupied this territory in Ham- 

 ilton time. It represents instead the acquisition of a new habitat 

 which had been outside the limits of its geographical range in the 

 Hamilton sea. The writer's study of the Devonian faunas in the 

 Allegheny region indicates that the typical Hamilton fauna with 

 T. carinatus does not extend as far to the southwest as Mountain 

 Grove, although the Hamilton sea extended much beyond that 

 point to the southwest. The occurrence of a Hamilton species 

 in abundance in the Chemung fauna of this part of Virginia thus 



