56 CONTRIBUTIONS TO DEVONIAN PALEONTOLOGY. [bull. 244. 
Other Hamilton species appear as low as the Marcellus; and, as has 
already been stated, there is evidence of a common fauna tying 
together the Genesee and Marcellus, thus suggesting a separation of 
the typical Tropidoleptus fauna of the Hamilton from the Buchiola 
speciosa fauna already mentioned. The Buchiola speciosa fauna is 
seen in greater purity and with a fuller list of species in the southern 
sections, where the black shale sediments dominate the column for a 
greater vertical extent than at the north. 
More facts are needed to fully differentiate these two faunas, but 
the dissections already made strongly suggest the probability that the 
faunas were contemporaneous over a great portion of their life history, 
and that the conditions of the sea bottom determined their geograph- 
ical distribution as well as the particular zones in the stratigraphical 
column in which the one or the other appears. 
The Buchiola fauna prevails wherever the Devonian black shale 
sedimentation was dominant, while the Tropidoleptus fauna exhibits its 
fullest development in the sediment composed of a fine-grained argilla- 
ceous mud, often more or less calcareous and typically rather light 
colored. A similar intercalation of two faunas is observed where the 
Trenton and Utica formations meet. 
In the Virginia area under consideration the Buchiola fauna ranges 
above as well as below the Spirifer disjunctus zone. In New York 
Spirifer disjunctus is generally regarded as strictly indicative of the 
higher part of the upper Devonian, but it is not restricted to this 
horizon in Iowa, Nevada, and Arizona if the morphological affinity of 
Spirifer whitneyi and S. disjunctus is recognized, as is necessary 
when an attempt is made to correlate American with European faunas. 
Nevertheless the lower limit of the Chemung may be well distinguished 
in eastern North America b}^ the first appearance there of Spirifer 
disjunctus and its normally associated fauna. 
The significance, therefore, of the prevalence in the region under 
investigation of the Buchiola fauna up to the first appearance of 
Spirifer disjunctus is found in the inference that not only the Tropi- 
doleptus fauna is there deficient, but that there is no distinct evi- 
dence of its immediate homeotopic successor, the fauna of the Ithaca 
member of New York. 
