120 CONTRIBTTIONS TO DEVONIAN PALEONTOLOGY. [bull. 244. 
Variation in No. <> occurs chiefly in relation to shape of muscular 
impression in pedicle valve and in the ratio of length and width. The 
two latter characters are equal in some individuals. In many the 
width exceeds the length by one-fourth or more. 
No. 9 shows considerable variability in this zone with reference to 
the number of plications. These vary from 13 to 29 on each valve. 
The length of the mesial septum is contained in the length of the shell 
from two to three and a half times. Of 23 specimens examined 
22 have one plication and one has a double plication in the sinus. 
All of the specimens show a double fold except one, which has a third 
plication weakly developed on the fold. 
Zone 15 of Mansfield section (1^59 B). — About 20 feet above the 
preceding faunule were found the following species: 
Faunule of zone 15 of Mansfield section (14-59 B). 
[a, abundant; c, common; r, rare.] 
1. Productella lachrymosa (c). 
2. Schizophoria striatula (r) . 
3. Camarotoechia stephani (a). 
4. Delthyris niesicostalis (a). 
5. Ainboccelia gregaria (r). 
6. Athyris angelica (r). 
7. Sphenotus contractus (c;. 
8. Edmondia philipi (c). 
9. Aviculopecten sp. (r). 
Zone 18 of Mansfield section (11^59 B). — One hundred and fifteen feet 
above zone 14 a thin calcareous bed appears, underlying the iron-ore 
bed. Only three species were collected from it. 
Faunule of zone 18 of Mansfield section (1459 B) . 
[a, abundant; c, common.] 
1. Productella lachrymosa (c). 
2. Camarotoechia stephani (c). 
3. Spirifer disjunctus (a). 
Zone 19 of Mansfield section (1\59 B). — Eighteen to 21 inches of red 
hematite comprise this zone. The only fossils found in it are Procbuc- 
tella lachrymosa and Spirifer disjunctus, which are common. 
Zone 21 of Mansfield section (1459 B). — Ten feet above the iron ore 
the highest faunule of the section appears. It contains the following 
species: 
Faunule of zone 21 of Mansfield section (1459 B) . 
[a, abundant: c, common; r, rare.] 
1. Orthothetes chemungensis (r). 13. Camarotoechia sappho (a). 
2. Productella lachrymosa (c). | 4. Spirifer disjunctus (c). 
