GENESEE SLATE. 
223 
The following species, figured in the Report of the Third District, page 168, are quite 
abundant in this rock in the eastern part of the district, but are far less common farther west, 
and disappear altogether before reaching Lake Erie. 
95. 
I. Orbicula Lodensis. 2. Atrypa (Orthis) quadricostata. 3. Lingula spatulata. 4. Lingula concentric®. 
1. Orbicula Lodensis. —The shell is concentrically striated, and marked by a few radiating 
lines. It differs from one in the Hamilton group, in being much smoother . 
Localities —Lodi in Seneca county, below the Falls; Big-stream point. 
2. Atrypa quadricostata. — Mesial portion of the shell marked by four or five strong ra¬ 
diating ribs ; sides nearly plain. 
Occurs with the last. 
3. Lingula spatulata. — This is an abundant little fossil in the localities named above, and 
js readily distinguished by its small size and spatulate form. 
4. Lingula concentrica. — This fossil is peculiar for its great proportional breadth at the 
beak, and the extent of the margin beyond. Some specimens seem scarcely referable to the 
genus. 
Occurs with the preceding species at Lodi, and near Bigstream point. 
For localities of superposition of this rock, see that head under Hamilton group 
