I'LATK V— ContinueJ. 

 Fig-. 19. The deltidial portion of tlie peilicle-valve ; sljowiTig- tlie broad delthyi-ium and the outline of the 



ninscrdar ai-ea which is not .sufficiently thicltenecl to obscure the plications of the shell. X 3. 

 Fig. 20. The area in the opposite valve; showing- the cai-dinal process, crural plates ami low median 

 i-iilge. X 3. 

 ..,,..; Hudson River g-rou|). Covington, Kentucky. 

 For further illustration, .see Pateontology of Ohio, Volume I, i^late viii, tig. 7. 



Orthis mcHOTOMA, Hall. 

 0. dic/io/.oma , Hall, = 0. fissicosla. Meek, not Hall. 



Fig. 21. The interior of the brachial valve; showing the cardinal process, ci-ural plates and the character 

 of the plications. 



Hudson River group. Covington, Kentucky. 

 Foi- fui-thei- illustration, see Palasontology of Ohio, Volume I, plate viii, fig. C, under the name of 

 0. fis.ncosta. 



Orthis Ella, Hall. 



Fig. 23. An individual viewed from the brachial valve, showing area and foramen of the opposite 



valve. X 2. . 



Fig. 23. A )ioition of the interior of the pedicle-valve ; sho-wing the chai-afiters of the cardinal area. X 3. 

 Hudson River gi-onp. Covington, Kentucky. 

 For further illusti-ation, see PalEEontology of Ohio, Volume I, plate viii, tig. 9. 



Ohthis Kaxkakensis, McCheslleJ^ 



Figs. 24, 25. Brachial and 2:iroHle views of a normal individual. 



Hudson River gi-ou^j. Wilmington, Illinois. 



Orthis Wiiitfieldi, N. TT. "Wineholl. 



Fig. 26. The interior of a pedicle-valve ; showing the relatively high area and strong teeth, the character 

 of the muscidar area, and the low ri<lges i-adiating from its anterior margin. 

 Hudson River group, fipring Valley, Minnesota. 



DINORTPnS, NOM. NOV. 



Page. 19.i. 



Orthis pectinella (Einmons), Ci)iinid. 



Figs. 27, 28. A view of the pedicle-valve, and profile of a specimen in which the i-ibs are more subdivided 

 toward the margin than is usual in the species. X 2. 

 Ti-enton limestone. Lewis county. New York. 

 Fig. 29. The interioi- of a small jjeilicle-valve; sho-wing the subqnadi-ate muscular ai-ea with the posterior 

 and anterior diductor and the adductor scars. 

 Trenton horizon. St. Paul, Miimesota. 

 Figs. 30, 31. A view from the pedicle-valve and the profile of a large inrli\-idual, showing the strongly ele- 

 vated, simple ribs. 

 Fig. 32. The intei-ior of a pedicle-valve. 

 Fig. 3)-^. The cardinal portion of a brachial valve. X 2. 



Ti-enton horizon. Curdsville, Kentucky. 

 For further illustration, see Palaeontology of New York, Volume I, plate xxxii, tig. 1''. 



Orthis Sweeneti, N. H. Winchell. 



Fig-. 34. Extei-ior of the pedicle-\-alve ; showing the depressed-con\-ex shell. 



Fig. 35. A profile of conjoined valves; in this figure the pedicle-valve as represented is too convex and too 



high at the head. - ' 



Fig. 36. The interior of the brachial valve.. i i.^ift-iiL'^ -io'3 



Trenton horizon St. Paul, Minnesota. 



OETHIS as resti-icted. 



Page lii-2. 



Orthis fl.4bellites, Hall. 



Figs. 37, 38, 39. The exterior of the pedicle and brachial valves and pi-ofile of an average specimen. 

 Fig. 40. The intei-ior of the pedicle-valve ; showing the character of the musculai- area. 

 Fig. 41. The interioi- of the brachial valve ; showing the cardinal process, crural plates and qnadiipartite 

 musculai- ai-ea. 



Niagara group. Lockport, N. Y. 

 For further illustration see Palfeontology of New Yoi-k, Volume II, plate lii, tigs. 6, 7. 



