TLATB V— Continued . 

 Fig-. 19. The lieltidial jiortioii of the peJicle-valve; showing the bi-oiul ilelthyrium ami the outline of the 



inn-icular area which is not sufficiently thickened to obscure the plications of the shell. X 3. 

 Fig:. -"• 'i"hH area in the oi)po.'iite valve ; showing- the cardinal i)i-oce.ss, crural plates ami low median 

 i-iilg-e. X 3. 



Hudson Rivei- group. Coinngtoii, Kentucky. 

 For further illustration, see Palieontology of Ohio, Volume I, plate viii, tig:. 7. 



Okthis niciiOTOMA, Hall. 

 (). <li(li(il<niiii, Iliill, = 0. Jissicosta. Meek, not Hall. 



Fig. 21. The interior of the bi-achial valve ; showing- the cardinal process, ciural plates and the character 

 of the ]ilications. 



Hudson River gi-ouj). Orvingtim, Kentucky. 

 For further illustration, see Palseontology of Ohio, Volume I, jilate viii. tig-, (i, under the name of 

 0. fis.tico.ita. 



Orthls Ei.r.A, Hall. 



Figf. 22. An indiviilual viewed from the brachial valve, showing area and foramen of the opposite 



valve. X 2. 

 Fig-. 23. A portion of the interior of the pedicle-valve; showing the characters of the cardinal area. X 3. 

 Hudson River gi-ouji. Coriiiffton, Kentucky. 

 For further illustration, see Palseontology of Ohio, Volume I, plate viii, fig. 9. 



Oiniii.-^ Kankakf,xsis, McChc'^noy. 



Figs. 24, 2.0. Brachial and profile views of a normal individual. 



Hudson River g-rouj). Wilmington, Illinois. 



Orthis Whitfieldi, N. H. WinolioU. 



Fig-. 26. The inteiior of a pedicle-valve ; showing the I'elatively high area and strong teeth, the character 

 of the muscidar ai'ea, and the low ridges radiating from its anterioi- marg-in. 

 Hudson River group. Spring Valley, Minncs-ota. 



DINORTHIS, NOM. NOV. 



Page. 19.-). 

 OUTHIS I'ECTINELLA (Eiiunoiis), Coiirad. 



Figs. 27, 28. A view of the pedicle-valve, and pj-otile of a specimen in which the riljs are more subdivided 

 towai'd the margin than is usual in the species. X 2. 

 Trenton limestone. Lewis county, Neio York. 

 Fig. 29. The interior of a small pedicle-valve; showing the subipiadratc muscular area with the posterior 

 and anterior diductor and the adductoi' scars. 

 Ti-enton horizon. St. Paul, Minnesota. 

 Figs. 30, 31. A view fi-om the pedicle-valve and the jirotile of a large individual, showing the strongly ele- 

 vated, simple ribs. 

 Fig. 32. The interior of a pedicle-valve. 

 Fig. 33. The cardinal portion of a brachial valve. X 2. 



Trenton horizon. Curdsville, Kentucky. 

 Foi- further illnsti-ation, see Palaeontology of New York, Volume I, plate xxxii, tig. I'. 



Orthis Saveeneyi, N. H. Wiiichell. 



Fig. 34. Exterior of the pedicle-valve ; showing the depressed-convex shell. 



Fig. 'if>. A ]>rotile of conjoined valves; in this tigure the pedicle-valve as represented is too convex and too 



high at the head. 

 Fig. 3G. The interior of the bi'achial valve. 



Trenton horizon tSt. Paul, Minncfota. 



ORTHIS ti.s rcstiicted. 



I'.'ige la-J. 



Orthis flabellites, Hall. 



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

 Fig. 40. The interior of the ])edicte-valve ; showing the character of the muscular area. 

 Fig. 41. The interior of the brachial valve ; showing the cardinal process, crural plates and (piadripartite 

 muscular area. 



Niagara grouj). Lockport, N. T. 

 For further illustration see Palseontology of New Ycnk, Volume II, plate Hi, figs. 6, 7. 



