WILLIAMS.] 
FAUNAL DISSECTION OF THE DEVONIAN. 
57 
formation at Caj^uga Lake, the dominant list already selected presents 
the most characteristic species on the basis of frequency of appearance 
vertically in the zones; but, allowing for imperfection in the collecting, 
the list as given in Table I may still stand as the list of dominant 
species of the fauna, considered geologically as well as geographically. 
EIGHTEENMILE CREEK SECTION. 
Another test of the correctness of the list of dominant species of 
the Tropidoleptus carinatus fauna is derived from a study of the lists 
of species reported by faunules as they occur in the section of the 
Hamilton rocks at Eighteenmile Creek. r/ 
Mr. Grabau made an exhaustive study of the zonal succession of 
faunules throughout the Hamilton of Eighteenmile Creek. In his 
list 35 zones are recognized. The total number of species named by 
Mr. Grabau in his list is 163, but 10 of these are not positively iden- 
tified with an}^ known species. Hence there are only 153 species 
positively recognized in the collections studied by him. Of these 
the following 12 are the more frequently represented in the zones, 
the first 9 of them appearing in at least 17 out of the 35 zones, or in 
50 per cent of the zones. 
Table III. — Tropidoleptus fauna: Twelve species occurring most frequent/!/ in 
the Hamilton formation at Eighteenmile Creek. 
[Dominant range frequency list for Eighteenmile Creek.] 
Number 
of zones 
in which 
found. 
Number 
of zones 
in which 
found. 
1 . Spirif er pennatus 
28 
7. Primitiopsis prmctilifera - - 
8. Stropheodonta perplana _ _ - 
9. Orthothetes arctistriatus ._ 
10. Rhipidomella vanuxemi--. 
1 1 . Productella spinnlicosta 
12. Cryphaetis boothi 
18 
2. Phacops rana . 
3. Chonetes lepidus 
26 
21 
20 
18 
18 
17 
17 
4. Athyris spirif eroides 
5. Ambocoelia umbonata 
6. Chonetes scitulus 
14 
14 
14 
It will be noticed that 4 of the species of this list belong to the 
dominant list of eastern New York (page 51), and these 1 are among 
the first 5 showing most frequent occurrence in the zones of the forma- 
tion in western New York, appearing in 18 or more of the 35 zones. 
It is to be noted, however, that several of the species of the list for 
eastern New York (Table I) are rare or wanting in the Eighteenmile 
Creek section, and are there restricted to a few zones. They are 
the following species, the number of zones in which they appear in 
the Eighteenmile Creek section being expressed by the figures to the 
right of the name. The total number of zones is 35. 
flThe faunas of the Hamilton group of Eighteenmile Creek and vicinity in western New York, 
by A. W Grabau: Sixteenth Ann. Rept. State Geologist New York, ]S«.),s. vv . ;>:{! 339. 
