PLATE LXXXIV. 
(Figures 1-4, 14-19, 23-25, 29, 31!, 37, 41-46 by G. B. SiMPSON ; 5-13, 20-22, 30-35, 38^0 by E. Emmons ; 25-28 copies.) 
Protorthis, sp. ? 
1. The interior of a pedicle-valve; showing the small spondylium made by the union of the short 
dental plates, the low median ridge and the muscular impressions. X 2. 
2. A portion of the same specimen drawn so as to show moi’e clearly the con Mergence of the dental 
lamellae. 
Calciferous horizon. Fm't Cassin, Vermont. 
ORTHOTROPIA, gen. nov. 
OrTHOTROPIA DOLOMITICA, S}). IIOV. 
B. Ventral view of an internal cast, natui'al size ; showing the form of the shell, the short, straight 
hinge, and the conspicuous muscular scai's. 
4. The interior of a xiedicle-valve ; showing the cardinal area, oiien delthyrium, muscular scar and 
short median septum. 
Ventral, dorsal and cardinal views (the last with the pedicle-valve above) of an internal cast; 
showing the form of the muscular impressions, the median septum in each \ alve, and the ele¬ 
vation of the cardinal area, X 2. The external surface of the shell is unknown. 
Niagara dolomites. Near Milwaukee, Wisconsin. 
The generic chai'acters of this shell are so distinctly unlike tho.se of any exi.sting genus that it is 
here proposed to distinguish it by the new term Orthotnopia. 
Orthis ? GLYPTA (Coiiipiire 0 . Loveni, Lindstroni), si), nov. 
8. A ]mrtial internal cast of the pedicle-valve ; showing the outline of the shell, its surface oi-namenta- 
tion and the foi'in of the muscular impression. 
9. A similarly preserved shell with but a single sei-ies of radial plications and showing tho x^eculiar 
reticulating sui'face sciilj^tui'e. X 2. 
Niagara dolomites. Near Milwaukee, Wiscojisin. 
Orthis flabellites, Hall, var. Spania , var. nov. 
See jjlates 5 and 20. 
Fig. 10. An internal cast of a pedicle-valve, having the expression of 0. flal>ellite.s, but with scarcely more 
than one-half of the number of j^lications usual in this species. 
Niagara dolomites. Near Mihoamkee. Wi,sco7isin. 
Stropheodonta (Pholidostrophia) nacrea, Hall. 
See Plate 15. 
Fig. 11. The interior of a brachial valve ; showing the muscular scars and vascular sinuses. X 2. 
Hamilton shales. Livonia Salt Shaft, New Yoi-k. 
Stropheodonta (Brachyprion) profunda, Hall. 
See Plates 12 and 20. 
Fig. 12. A portion of an internal cast of a large pedicle-valve ; showing the cardinal area, the partial filling 
of the delthyrium, the small adductor and large diductor impressions. 
Niagara dolomites. Near Milwaukee, Wisconsin. 
Stropheodonta (Douvillina) Cayuta, Hall. 
See Plate 15. 
Fig. 13. The interior of a pedicle-valve; showing the elevation of the muscular scar into a well defined 
jilatform ; also the abrasion of the caj’din.al area by the teeth of the opxiosite valve. 
Chemung grouj). Steuben county. New York. 
Stropheodonta (Brachyprion) corrugata. Hall. 
See Plate 15. 
Fig. 14. A portion of an internal cast of the pedicle-valve enlarged to show the crenulations of the hinge- 
plate, near the beak. X 2. 
Clinton group. Rochester, New York. 
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