WILLIAMS. I 
FAUNAL DISSECTION OF THF DEVONIAN. 
85 
species at different times, according to the order in which he happens 
to take them up for study. In Schuchert's list « there are 15 species 
of Prodicctella recognized as belonging to the Chemung fauna. Spiri- 
fersof the three types — disjunctus, mesicostalis, and mesislridlis — are 
present and each type is widely variable. The rhynchonellas of the 
contractu, sappho, and eximia types are all very variable, the last 
appearing more conspicuously below and the others higher; but 
between the several species named frequent intermediate forms are 
found which it is difficult to determine specifically. Chonetes scitulus 
and Chonetes setigera are extremely difficult to discriminate. A foot- 
note to Plate VI, A, of Hall and Clarke's revision of the Brachiopoda, 
contains the following statement about the orthids: 
The species of Orthis=Schizophoria, described as O. propinqua, O. tulliensis, 
O. impressa, O. ioivensis. and O. macfarlanii, present so many features in com- 
mon that further study and comparison should be given them to determine the 
actual value of the characters on which the specific distinction has been based, 
and whether these differences coincide with their geological relations. 
These remarks will suggest an explanation for some of the differ- 
ences observed in the lists of Chemung fossils reported by different 
authors. Nevertheless, it seems reasonable to rely on the value of 
frequency of appearance in recorded lists (made by the same author) 
of the species of separate faunules as evidence of a corresponding 
frequency of the species in the actual faunules. 
In the following table the statistics reported for the Genesee Valley 
faunules are given. In this case the failure to mention the less com- 
mon species in every faunule list arose from the fact that the chief 
purpose of the report as made was to distinguish the successive zones 
into which the fauna was divisible. The lists are sufficient, however, 
to indicate the dominant species. 
Table XIX. — Spirifer disjunctus fauna: Dominant species of the fauna as 
occurs in the Oenesee Valley section. 
Species. 
Thirty- 
seven 
locali- 
ties. 
Species. 
Thirty- 
seven 
locali- 
ties. 
1. Spirifer disjunctus 
24 
16 
12 
10 
9 
7 
7. Productella lachrymosa and 
vars 
21 
var 
3. Athyris angelica 
4. Orthothetes chemungensis 
5. Delthyris mesicostalis 
6. Schizophoria striatula impressa 
8. Amboccelia umbonata : 
9. Sphenotus contractus 
10. Chonetes scitulus 
7 
7 
7 
11. Mytilarca chemungensis 
1 2 . Grammy sia c< >mmunis 
C 
4 
A list of the species of the Chemung formation of Chautauqua 
County (prepared by G. D. Harris in 18X7), indicating the dominant 
«A synopsis of American fossil Brachiopoda, including bibliography and synonymy: Bull. 
U. S. Geol. Survey No. 87, 1897, pp. 1-464. 
