PLATE LXXXL 



IFiguic- 1-3. 5-'il, 5B. 2SI-I3 liy E Kmmox.s ; ( Ijy U. B Simpson ; -22- .'5, 27, W by II. 1*. WiiitfikU) ) 



Genus DIELASMA. King. 



I'age -I'xt. 



DlELASMA TURGIDA, ILlll. 



Figs. 1-3. Dorsal, ventral and profile views of an average specimen with median sinus on both valves. 

 Fig. 4. Profile of an old shell with hitrbly ventrieo.«e valves. 



St. Louis group- Wax/iingtim county, Indiana. 

 Figs, .5, ti. Front and dorsal views of a small shell having the median sinus very broad. X 2- 

 Figs. 7, 8 Front and dorsal views of a specimen having a .single plication in the sinus of the pedicle-valve 

 and a corresponding groove on the opposite valve. X H- 



Chester group, fipeneer cimnlij, Indlann 



DiEl.ASMA BUKLINGTO.NEXSIS, Wililc. 



Figs. 9-11 Pnrsal, profile and ventral views of a small shell. 



(I"hert of the Burlingtim limestone. Lnititilaiui; MixKoiiri. 



DiKLASMA FORMOSA, Htlll. 



Figs. 12, 13. Profile and dorsal views of a small internal cist. 



Fig. 14. Profile of a shell of about the same size, but with mure gibbous valves. 



Fig. 13. Dorsal view of an internal cast ; showing that in these small shells the muscular jilatfoi'm of the 



brachial valve is not clearly defined. 

 St. Louis gi'oup. 

 Fig. 16. A cast of the cardinal jiortion of the pedicle-\alve. enlarged to show the cavity left by the enfolded 



margin of the pedicle-passage, the dental lamella; and deltiilial plates. X 2. 

 Fig. 17. An internal cast of the brachial waive ; showing the impression left by the base of the musculai- 



platform, and the genital markings about the muscular area. 

 Figs. 18, 19. Profile and dorsal views of a specimen of medium size. 



St. Louis group. 

 Fig. 20. Dorsal view of a large individual retaining the shell. 

 Fig. 21. Doreal view of a specimen cut to expose the loop. 

 Figs. 22, 23. Ventral and dorsal views of the loop of the same specimen enlarged. As is usual in these 



shells the recurved lamella is not perfectly retained 

 Fig 24. Dorsal view of a large internal cast ; showing a portion of the Viase of the muscular jilatform, and 



divergent, probably vascular impressions ovei' the adjoining surface. 

 Figs 25, 26. Profile and dorsal views of a characteristic and somewhat gibbous example. 

 St. Louis group. 



DlELASMA ROWLEVI, \\'()rthoil. 



Figs. 27, 28. Profile and dorsal views of an internal cast, referred with hesitation t(> this species ; showing 

 the muscular plattVirm of the lirachial valve, and the cavities of th(' dental lamellie. 

 Choteau limestone. Cfraydan Springs, Minsvuri. 



DlELASMA BOVIDENS, Moftoil, 



Figs. 29, 30. Dorsal ami pi-ofile views of a rather gibbous specimen ; showing the contour of the valves and 

 the i.jblique foramen The concentric surface lines appear to be to some extent color-markings, 

 and not infrecjuently faint traces of a radial coloration are discernible in the shelLs. This 

 specimen is of about the average size of the species as it oceui's at this locality. 

 Upjier Carbonifei-ous. Kansas Oity,J!i'IUsouri. 



