PLATE LXXXIV. 



(Figures !-♦, 14-1!1. 23-25, 29, 3r,, 37, 41-46 by G. B. Simpson ; .V13, 20-22, 30-36, 38-40 liy E, KMMONS ; 2.i-28 copies.) 



Protorthis, sp. ? 



Fig-. 1. The interior of a pedicle-valve ; showing' the small spondyliinn made by the vinion of the short 

 dental plates, the low median ridge and the muscular impressions X 2. 



FifT. 2. A portion of the same specimen drawn so as to .show nioi'o clearly the converg-ence of the <lental 

 lamella?. 



Calciferoua hori/on. I^trt Cafis-iii, Vei-nwnl. 



ORTHOTROPIA, grn. nov. 



OrTHOTROPIA DOLOMITICA, .sp. 1U)\ . 



Fig. 8. Ventral view of an internal cast, natni-al size ; showing- th(> fonu of tin- shell, the .short, straight 



hinge, and the conspicuous muscular scars. 

 Fig. 4. The interior of a pedicle-valve ; showing- the cardinal area, open dcltliyiiini], niusi-ular scar and 



short meilian septum. 

 Figs. 5-7. Ventral, doi-sal and canlinal views (thi' last wilh the pi'dicle-valve above) of an internal cast; 

 showing the form of the mu.--cular imjiressions, the median septimi in each valve, and the ele- 

 vation of the cardinal area, X 2. Tin' external surface of the shell is unknown. 

 Niagara dolomites. Near MUwaiikrc. Wisconsin. 

 The genei'ic chai-acters of this shell are so distinctly unlike tho.se of any exi.sting genus that it is 

 here proposed to distinguish it liy the new lerni OrthcitmiI'ia. 



Orthi.s ? GLYPTA (C<>iHi):irc 0. Loveni, Lin(l.->tioiii), sp. iiov. 



Fig. H. A partial internal cast of the pediidi!-valve ; showing the outline of the .shell, its surface ornamenta- 

 tion and the form of the muscular impression. 



Fig. !). A similarly preserved shell with but a sing-le .sej'ies of radial jilications and showing tho pecidiar 

 reticulating surface sculptiu-e. X 2. 



Niagara dolomites. Near Milwaukee, IViicoiiMn. 



Orthis flabellites, Hall, var. Sjxniia, var. iiox-. 

 See plates 5 and 20. 

 Fig. 1(1. An internal cast of a pedicle-valve, having the expression of 0. JlaheUite.t, but with scarcely more 

 than one-half of the number of jilications itsual in this species. 

 Niagara dolomites. Near Milwaukee. Wiseunsin. 



Stropheodonta (Pholidostrophia) nacrea, Hall. 



See Plate 1."). 

 Fig. 11. The interior of a brachial valve ; showing the muscular scars and vascular sinuses. X 2. 

 Hamilton shales. Livonia Salt iihaft, Neio York. 



Stropheodonta (Brachypuion) profunda, Hall. 



See Plates 12 and ■20. 

 Fig. 12. A piu'tlon of an internal cast of a large pedicle-valve ; showing the cardinal area, the partial filling 

 of the delthyrium, the .'imall adductor and large diductor impressions. 

 Niagara dolomites. Near MilvMukee, Wiseon.nn. 



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 deKned 

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

 Chemimg group. Steuben county. New York. 



Stropheodonta (Brachyprion) corruoata, 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. 



