WILLIAMS.] 
FAUNAL DISSECTION OF THE DEVONIAN. 
77 
doubtful specific identification, and only one other case of a Produc- 
tella is reported. This suggests, in connection with its standing 
second in dominance in the list for the Ithaca formation at Ithaca, 
that the immigration of the fauna was from the west, and that it had 
not so strongly occupied the eastern area as that of central New York 
at this horizon. 
Analysis of this list shows that two of the dominant species of the 
Tropidoleptus fauna are still dominant, but the other species of the 
list have dropped out. Among the species of the list which occur in 
the Tropidoleptus fauna, but are there rare, are Actinopteria boydi 
and Paracyclas Virata. These, though frequent in the faunules occur- 
ring east of Fulton, Schoharie County, are rare in the Hamilton for- 
mation west of that point. Cy'pricar delta gregaria, though occa- 
sional, is very rare in the eastern Hamilton faunules. Another 
species of the genus, C. bellistriata, is common in the Hamilton for- 
mation. 
It is evident, therefore, upon purely paleontological grounds, that 
this fauna, classified as of the Ithaca formation, is distinct from and 
later than the Tropidoleptus fauna of the Hamilton formation, and 
this is evident in spite of the fact that it contains all of the 12 domi- 
nant species of the latter fauna. The discrimination between the two 
is based upon a change in the bionic values of the dominant species 
and upon the introduction of new species or varieties which are either 
rare or wanting in the typical Tropidoleptus fauna. 
The correctness of this interpretation is further supported by the 
presence of species entirely wanting in the underlying Hamilton for- 
mation of the region, but present in the Ithaca formation at its typ- 
ical expression in Tompkins County. 
Table XVI is compiled from the statist ics reported by Prosser in 
the papers already referred to: 
Table XVI. — Productella speciosa fauna: Twenty-one species characteristic of 
the Ithaca formation of eastern Neiv York and Pennsylvania not occurring in 
the Tropidoleptus fauna. 
[The starred species are dominant at Ithaca. | 
* 1. Camaroteechia stephani. 
* 2. C. eximia. 
3. Cryptonella eudora. 
* 4. Leiorhyiichus mesicostale. 
5. Orbiculoidea media. 
6. O. neglecta. 
* 7. Productella speciosa. 
* 8. Spirifer mesistrialis. - 
* 9. S. pennatus var. posterns. 
10. Actinopteria perstrialis. 
11. A. theta. 
12. Grammy sia elliptica. 
13. G. globosa. 
14. G. nodocostata. 
15. Leda brevirostris. 
Lrmulicardinm ornal us. 
Modiomorpha subalata var. 
mungensis. 
Prothyris lanceolata. 
Pterinopecten sul >< >rl >icularis. 
20. Schizodus ellipticus. 
21. Coleoms acicumm. 
16 
*17 
18 
19 
che- 
Of these 21 species not in the Tropidoleptus fauna appear also 
in the Portage list. 
