632 SLOARD WEEE ET: 
4. Bellerophon sp. (r). 
5. Gyroceras cf. trivolve Conrad (r). 
6. Tentaculites bellulus Hall? (c). 
7. Phacops rana Green (c). 
8. Proetus canaliculatus Hall (r). 
9. Zaphrentis sp. (x). 
0. Cystodictya sp. (Cc). 
5A*, Four inches of impure brown limestone like the last, but with few 
specimens of Chonetes coronata. 
1. Orthothetes chemungensts Conrad var pandora Billings (r) . 
2. Chonetes coronata Hall (c). 
3. Spirifer fornaculus M. & W. (a). 
4. Gomphoceras sp. (r). 
DISCUSSION OF THE FAUNAS. 
From a general survey of the entire fauna of the section, 
seven conspicuous divisions may be recognized. The first of 
these include zones 5A’ and 5A? The conspicuous species are 
Orthis (Rhiphidomella) semele ? and Platyceras sp. Orthis (Riupid.) 
semele was originally described by Hall from very imperfect 
material found in the Onondaga limestone in Erie county, N. Y. 
The Illinois specimens are not perfectly preserved, but seem to 
agree more nearly with this species than with any other. The 
Platyceras is of a type which might be present in any fauna from 
the Lower Helderberg to the Hamilton inclusive. Well preserved 
specimens of spirifer macrothyris and spirifer raricostus are present, 
which are good Upper Helderberg species. Associated with these 
are Nucleospira ventricosa and Nucleospira elegans? which were 
described from the Lower Helderberg, and an undescribed 
species of Zatonta, which genus has not hitherto been recognized 
above the Oriskany. There is no fauna comparable to this one 
in the western interior Devonian province, but in the eastern 
province this association of species is about equivalent to the 
lower half of the Upper Helderberg group in the New York 
series. 
The second division of the general fauna includes zones 5A* 
to 5A. The association of species in these zones is a typical 
