86 CORRELATION OF GEOLOGICAL FAUNAS. [bull. 210. 
species in each fanmile, shows the following species to be dominant 
in approximately the order in which they are listed below: 
Table XX. — Spirifer disjunctus fauna: Dominant species of the Chautauqua 
County faunules. 
1. Camarotoechia contracta. 
2. Spirifer disjunctus. 
3. Amboccelia gregaria. 
4. Camarotoechia duplicata. 
5. Dalmanella leonensis. 
6. Chonetes scitulus. 
7. Productella hystricula. 
8. Athyris angelica. 
9. A. polita. 
10. Productella lachrymosa. 
11. Palaeoneilo constricta. 
12. Orthothetes chemungensis. 
Examination of these lists in respect to the less common but char- 
acteristic species brings out some peculiarities in geographical distri- 
bution which should be here indicated. Orthids of the Sehizophoria 
type, like impressa and tioga, are more conspicuous in the eastern 
than in the western faunules of the State, and in range they are con-" 
spicuous in the lower rather than in the higher portions of the sec- 
tions. Spirifer mesistrialis is less conspicuous in the western than 
in the middle and eastern part of the State, where it appears as low 
as the Ithaca formation. Delthyris mesicostalis of the characteristic 
form is conspicuous in the Genesee Valley faunules of the Chemung, 
but is infrequent in the Chautauqua County sections. Camarotoechia 
contracta and C. duplicata and Athyris angelica and A. polita are of 
frequent occurrence in the purer Chemung faunas of the western part 
of the State and become less conspicuous in the eastern faunules. 
When the attempt is made to construct a standard list of dominant 
species of the Spirifer disjunctus fauna, after the first half dozen com- 
mon species, there is a much larger number of species which are domi- 
nant in some part of the region, or in some part of the formation, 
though not characteristic of all the formation or of the whole area of 
western New York alone. 
From the statistics now in hand we may form the following stand- 
ard list of dominant species of the fauna, which, may be divided into 
three parts: (1) The first six species are dominant throughout western 
New York localities, and, stratigraphically, throughout the successive 
zones of the formation; (2) the species numbered 7 to 11 are more 
dominant in the eastern localities in middle New York; while (3) the 
remaining species numbered 12-20 are more common in the western 
counties of the State. 
Table XXL— Spirifer disjunctus fauna: Standard list of dominant species of 
the Spirifer disjunctus fauna for the New York province. 
1. Spirifer disjunctus. 11. Atrypa spinosa hystrix. 
2. Camarotoechia contracta. 12. Orthis (Sehizophoria) impressa. 
3. Amboccelia umbonata. 13. Athyris angelica and polita. 
4. Orthothetes chemungensis. 14. Sphenotus contractus. 
5. Productella lachrymosa and vars. 15. Mytilarca chemungensis. 
6. Delthyris mesicostalis. 16. Grammysia communis. 
7. Spirifer mesistrialis. 17. Chonetes scitulus. 
8. Orthis (Sehizophoria) tioga. 18. Camarotoechia duplicata. 
9. O. (S.) carinata. 19. Dalmanella leonensis. 
10. Pterinea chemungensis. 20. Palaeoneilo constricta. 
