80 PALEOZOIC PALEONTOLOGY. 
The conditions which obtained in the region under discussion dur- 
ing the time of deposition of the Rondout formation were peculiar, 
as is shown by the almost entire absence of all organisms except 
ostracodes belonging to the genus Leperditia. In the earlier report 
it was suggested that these ostracode faunas in some way represented 
the Hurypterus fauna of the “waterline” formation of Western New 
York, but it now seems clear that the New Jersey formations of this 
period were deposited in a distinct basin, which probably had no 
direct connection with the contemporaneous interior sea. It is pos- 
sible that these Leperditia faunas lived under non-marine, perhaps 
brackish water conditions, as was formerly suggested, although these 
conditions may have been more or less local, and may not have existed 
throughout the entire Cumberland basin. At any rate, in that portion 
of the Cumberland basin which is now included in New Jersey, the 
conditions were not favorable during Rondout time for the existence 
of the typical marine faunas of the period, with an abundance of 
brachiopods, trilobites, &e. Brachiopods did exist, however, in this 
portion of the Cumberland basin at this time, though rarely, as is 
shown by the presence of Hyattella? lamellosa. 
In the lower beds of the Manlius limestone there is evidence of 
environmental conditions similar to those of the Rondout. Leperditia 
still remains the most common form of life, but associated with this 
ostracode are other organisms, especially stromatoporoids, and an occa- 
sional pelecypod. In the middle portion of the formation Leperditia 
is still abundant, but is associated with a brachiopod fauna prolific in 
individuals, which suggests the recurrence of more typical marine 
conditions of environment. In the upper beds of the formation 
Leperditia has entirely disappeared and the fauna has assumed an 
entirely normal marine aspect. In this fauna the most characteristic 
species is Spirifer vanuxemi, which was represented by a varietal 
form in the Decker Ferry fauna. 
The greatest faunal change is to be found in passing from the 
Manlius to the Coeymans limestone, and the Coeymans fauna repre- 
sents the first distinctive immigration of an important, typically 
marine fauna into the northern portion of the Cumberland basin 
since its occupation by the Decker Ferry faunas. The importance 
of this immigration seems to be sufficient to be recognized as the 
beginning of the period which we call Devonian time, the Coeymans 
fauna being the earliest of the Helderbergian faunas in America, all 
of which have distinctively Devonian characteristics. 
