PLATE IV c. 



Legenil. ii. Doltidium. 



b. Deltiiiial slope. 



c. Deltiiiial ridges, 

 ca. Cariiiiial iiiea. 

 eg. Car<liual groove. 

 CI-. Crescent. 



d. Areal hordeivs. 



h. Cardinal buttre.ss. 

 i. Uuiboual ehamber.s. 



Fig. 



j. Platform. 



k. Platform- vaults. 



11. Median scai-s. 



II. Anterior scars. 



o. Lateral scars. 



(|. Crown of crescent. 



r. Side of crescent. 



n. Pallial trunk.';. 



i'. Secondary [lallial sinuses. 



MONOMERELLA, Billings. 



Page 40. 



MoNOMERELLA Nevvberryi, HhU iiiid Whittield. 



An internal cast of the brachial valve, indicating- a strong crescent ami low nmbonal chambei-s. 

 The reveree of the same specimen ; showing the short umbonal chainbei's and the deep cardinal 



gi'oove. 



Niagara limestone. Q-enoa, Ohio. 



Fig. 

 Fig. 



Fig. 



MONOMERELLA (clif. < JUBICULAUIS, Billillgs). 



3. Profile view of an internal cast. 



4. Another view of the same specimen ; showing the internal features of the pedicle-valve. The 



cardinal groove and the crescent are very conspicuous, the umbonal chambers sliort, scarcely 

 reaching the hinge, and the lateral muscular impressions very shai'ply developed. 

 0. The opposite side of the same specimen ; showing the low umbonal chamber, the strong crescent, 

 and incipient plafform-vaults. 



Niiigara limestone. Between &rafUm and Cedarburg, Wlseon.mi. 



MONOMERELLA PRISCA, Billillg.S. 



Fig. 6. An internal east of a portion of the pedicle- valve, in which the caj-dinal .irea is very high and the 

 platform slightly unsymmetrical. 



Fig. 7. The interior of a pedicle- valve, drawn from a gutta-percha impression of the spei^imen represented 



in tig. C, anil slightly restored about the anterior jiortion. 

 Fig. 8. The intei-ior of a pedicle-valve, in which the deltidiuui is narrow and elevated, the deltidial ridges 



obscure, and the .areal borders smooth. From a gutta-percha impression of a natui'al cast. 

 Fig. 9. An internal cast of a pedicle-valve, in which the umbon.al chambei-s have iheir usual length. 



The crescent and lateral scars of the phitform are unusually distinct. 

 Fig. 10. An internal cast of the pedicle-valve, in which the umbonal chambei-s are of unequal length. 

 Fig. 11. An intei-nal cast of both valves, to which a jiortion of the mati-ix adheres; showing the thickness 



of the shell in the umbonal regions. 

 Fig. 12. An internal cast of a brachial viilve, with indistinct radiating, probably v.-isciilar furrows in the 



anterior region. 



Fig. 13. All intei-nal cast of a brachial valve ; showing the characteristic markings of the .shell. 

 Niagara limestone. Hmothorne, Illinois. 



MONOM ERELLA O RTON I 



sp. UOV. 



Fig. 14. An internal cast of the pedicle-valve, in which all the characters of the shell are very .sharply 

 defined. 



Fig. 15. The counterpart of the same valve, from a gntta-jiercha imi)ression ; showing the broad deltidium 

 without evidence of subdivision, the conspicuous cardinal slope and groove, the crescent and 

 platfonn scars and the pallial trunks with their ramifications. 

 Niagara limestone. liisiny Sun, Ohio. 



