APPENDIX, Containing additional Descriptions of Fossils of the Ta- conic and Lower Silurian Systems. GASTEROPODA. Stkaparollus planistria (Hall). PI. 4,.fig. 16, 17. Shell small, depressed: volutions three or four; outer volu tion sharply angular; striae flat and plain. Bellerophon profundus. PI. 17,fig. 7. Volutions about three, contiguous, marginated, direct, gradu ally increasing in size; umbilicus deep; aperture somewhat lunate. Watertown, in the lower part of the Trenton limestone. Pleurotomaria percarinata. PI. 5, Jig. 7. This fossil is found in the Trenton limestone at Middleville, associated with Atrypa hemiplicata, Cyrtolites compressus, and C. trentonensis, fig. 22. The gasteropoda of this locality though numerous, are rarely smooth and perfect, and hence there is some difficulty in identifying them. P. suetilistriata. PI. 6, fig. 11, 12. Small, conical; spire depressed; volutions four or five; smooth, or the strirn extremely fine; aperture transverse and subtriangular. Trenton limestone. 30