No. 514] 



DISK II THY J I) ARMOR PLATES 



51)7 



locality. These limestones then give us the history of 

 areas in the old Marcellus sea which were covered from 

 time to time by invading faunas. It is natural therefore 

 that we should find a species of Dinichthys probably one 

 of the most mobile animals of the time associated: (1) 

 in one locality with the large cephalopods of the Agoni- 

 atites Limestone, (2) in another with the small hraehio- 

 pods and pelecypods of the typical black shah' and prob- 

 ably not far from an area occupied by the Stafford fauna 

 and (3) in the unfossiliferous black shale from which 

 the present specimen came. 



In his paper cited above Dr. Clarke brings out evidence 

 to show that the Agoniatites Limestone and some of the 

 lower Marcellus black shale in central and eastern New 

 York is the time equivalent of some of the upper Onon- 

 daga of the western portion of the state. This lends a 

 peculiar interest to the Onondaga County specimens of 

 D. halmodeus which coming as they do from the lower 

 Marcellus lived in a muddy portion of the great New 

 York embayment at no great distance from an area to the 

 west in which Onondaga Limestone conditions prevailed. 

 It is therefore not unreasonable to expect that D. hal- 

 modeus or some very closely related form may in time 

 be found in the upper Onondaga deposits of this latter 

 region. 



