The Galena and 3faquoketa Series. — Sardeson. 109 
that is found in the Trenton of New York. In the Galena 
and Maquoketa series it is the only Platystrophia wherever 
yet found. But in New York and Ohio it belongs to the 
Trenton group. Other species or varieties, O. lynx Eichw. 
O. acutilirata Conrad, 0. laticostata Meek, et al. take its 
place in the Hudson shales. All the Platystrophia are con- 
temporaneous species, or practically so in the Hudson epoch, 
and are distinct. The Trenton representative is the prede- 
cessor, too, of all the Hudson species, and may be the parent 
species of all. It is a synthetic type as compared to them. 
Again, in O. bellarugosa Conrad of the Galena series, and 0. 
insculpta Hall of the Maquoketa, we have two unique nearly 
like forms with mere varietal differences perhaps. In them as 
in those of Platystrophia and 'Orthis testudinaria,^ a close 
phylogenetic relationship is apparent, while so far as repre- 
sented by specimens of fossils" in collection the species all, or 
varieties, whichever they be called, are distinct. 
DESCRIPTION OF PLATES. 
Plate IV. 
Orthis rogata Sardeson fig. 1 to 10. 
Fig. 1. Ventral view of an average sized shell, from theFucoid bed. 
Fig. 2. Ventral view of small shell, base of Ovthisina bed, (X 10). 
Fig. 3. Analysis of ventral plication of specimen from the Fucoid 
bed. 
Fig. 4. Exact median, longitudinal section. Fucoid bed. 
Fig. 5. Same as fig. 4 with the parts of the shell analyzed. 
Fig. 6. Interior outline of a dorsal valve, to show the muscle scars, 
septum and crura. Orthisina bed. 
Fig. 7. Interior of dorsal valve. Fucoid bed. 
Fig. 8. Cardinal area, crura and cardinal process, same as fig. G. 
(X2.) 
Fig. 9. Cast taken from interior of a ventral valve. Fucoid bed. 
Fig. 10. Natural cast of another specimen. Fucoid bed. 
Numbers 1, 2, 3, 4, 5, 7, are from Ellsworth, Wisconsin; 2, 9, 10, are 
from Saint Paul: and 6, 8, are from Berne P. O., Minnesota. 
Orthis corpulenta Sardeson, fig. 11 to 19. 
Fig. 11. Dorsal view of a large specimen. Leptaena bed. 
Fig. 12. Lateral profile. Lept;ena bed. 
Fig, 13. Ventral view small, young specimen. Leptiena bed. 
Fig. 14. Analysis of ventral plication of an average specimen, from 
the Leptsena bod. 
Fig. 15. Interior of dorsal valve, in outline. Triplecia bed. 
Fig. 1(J. Same as last, shaded. 
