Williams.] FAUNAX DISSECTION OF THE DEVONIAN. 83 
disjunctus fauna, and the formation through which this fauna prevails 
is the Chemung formation. 
SPIRIFER DISJUNCTUS FAUNA. 
The fauna of this typical Chemung formation, as it appears in the 
southern tier of counties in the western half of New York State, may 
be appropriately called the Spirifer disjunctus fauna from the brach- 
iopod species of that name which is abundantly represented in the 
rocks of the formation and is widely distributed elsewhere. 
In 1884, in Bulletin No. 3, the fauna was critically separated from 
the fauna occuring below it, south of Ithaca, and the name disjunc- 
tus fauna was applied to it. The original list of species of the f : tu- 
nnies examined in the counties directly south of Cayuga Lake (as then 
identified) included 46 species. 
In a preliminary "Catalogue of the fossils of the Chemung period 
of North America,"" published two years before, in November, 1882, 
a list was given containing 94 genera with 268 species and varieties. 
Since then the New York State paleontologist has published revisions 
of the Lamellibranchiata, the Brachiopoda, and the Crustacea of the 
Devonian formations of the State, and it is quite probable that now 
the number of genera may have increased to 150 and the species 
to 400, or perhaps 500; but the literature in which the species are 
described gives very little evidence upon which to base a definite 
estimate of the bionic values of these species — either the bionic 
value as expressed in terms of frequency of individuals in the local 
composition of the faunas, or that expressed in terms of frequency 
of appearance in geographical distribution.^ 
The first attempt to form a list of the dominant species of the dis- 
junctus fauna, purely on the basis of what I have, in the presenl 
paper, denominated bionic values of the species, was made in 1884, 
in a paper on the Ithaca faunas. c 
The following list was prepared on that basis, as roughly estimated 
in the field, without, however, recording the exact statistics of abun- 
dance and frequency, statistics which have been insisted on in later 
investigations. 
Table XVIII.— Spirifer disjunctus fauna: Dominant species of the Chemung 
, formation south of Ithaca, N. Y. {roughly estimated in the field) . 
1. Schizophoria tioga. 
2. S. carinata. 
3. Stropheodonta mucronata. 
4. Productella lachrymosa. 
5. Spirifer disjunctus. 
6. Atrypa spinosa hystrix. 
7. Spirifer mesistrialis. 
8. Ambocoelia gregaria. 
9. Spirifer (Delthyris) mesicostalis. 
10. Orthothetes clienmngensis. 
11. Pteiinea chemungensis. 
12. Camarotoechia contracta. 
The twelfth species is not mentioned in my List from station 72, 
near Park station of the Utica, Ithaca and Elmira Railroad (p. 22), 
"University Press, Cornell University, Ithaca, N. Y. 
&See the discussion of bionic values of fossils, p. 124. 
o Bull. U. S. Geol. Survey No. 3, 1884, pp. 22-23. 
