PLATE LXXXIV. 



(FUcviW' l-«. •♦-•»• **-*■ *»' *'■'• *'• *'-•* ^y ^' ••■ ■'''MP80N ; 5-1:1, 20-J2, :tO-.1«, S8-W liy E. Kmmonr ; 2.V28 copies.) 



Protorthis, sp. ? 



Vig. 1. The int<>rior of a i>eilicle-valve; showinjr the siiiall sjtomly limn made by the union of the short 

 <lent«l plates, the low median ridge and the muscular imiireasions. X 2. 



Fig. 3. A portion of the same specimen drawn so as to show more clearly Ihe converg'ence of the dental 

 lamellie. 



Calciferous horizon. M>rt Can/tin, Veniumt. 



ORTHOTROPIA, okn. nov. 



ORTHOTROriA DOLOMITICA, 6\). IIOV. 



Fi(j. 3. Ventral view of an internal cast, nat II I'lil t^izo ; showinji' the fonn of the shell, the short, straigfht 



hing«, and the conspicuous mus(Milar si'nrs. 

 Pig'. 4. The interior of a jiedicle-valve ; showinjr the cawlinal are*, open ilelthyrium, muscular scar and 



short raeiiian septum. 

 V\ga. 6-7. Ventral, dorsal and caniinal views (the last with the peilicle-valve ahove) of an internal cast; 

 showing the fonn of the muwHilar impi-essions, the median septum in ea<;h \alve, and the ele- 

 vation of the carilinal area, X 2. The external surface of the shell is vinknown. 

 Niagrara dolomites. Near Milimukee. M'iscongin. 

 The generic charactei'S of this shell ai-e so distinctly unlike those of any existing genus that it is 

 here proposed to distinguish it by the new tei-m Orthotropia. 



Orthi.s ? OLYPTA (C(H)ipare 0. Loieni, Liiulstioni), sp. iiov. 



Fig. S. A jiartial internal cast of the pedicle-valve ; showing the outline of the shell, its surface ornamenta- 

 tion and the fomi of the muscular imju-ession. 



Fig. 9. A similarly preserved shell with but a single series of radial plications and showing tho peculiar 

 reticulating surface sculptui'e. X 2. 



Niagara dolomites. Near Milwaukee, WiscoTisin. 



Orthis FLABELLITE8, Hall, var. Sjmnia, var. llo\^ 

 See plates 5 and 20. 

 Fig. 10. An internal cast of a pedicle-valve, having the expi-ession of 0. jlabeUites, but with scarcely more 

 than one-half of the number of plications usual in this species. 

 Niagara dolomites. Near Milicaukee, Wisconsin. 



Stropheodonta (Pholidostroi'hia) 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 fialt iSliaft, Neic York. 



Stropheodonta (Brachyprion) profunda, Hall. 



See Plates 12 and 20. 

 Pig. 12. A portion of an internal cast of a large pedicle-valve ; showing the cardinal ai-ea, the partial tilling 



of the delthyrium, the small adilui-tor and large diductor impressions. 

 "  "' Niagara dolomites. Near Milwaukee, WiseoTUii7i. 



Stropheodonta (Douvillina) Cayuta, Hall. 



See Plate 1.5. 

 Pig. 13. The interior of a pedicle-valve ; showing the elevation of the mu.scular .scar into a well defined 

 platform j also the abrasion of the cardinal area by the teeth of the opposite valve. 

 Chemung group. Steuben county. New York. 



Stropheodonta (Brachyprion) corruoata, Hail. 



See Plate Mi. 

 Fig. 14. A jxjrtion of an internal cast of the pedicle-valve enlarged to show the crenulations of the hinge- 

 plate, near the lieak. X 2. 



Clinton group. Rochester, New York. 



