PLATE LXXXI. 
(Fisures 1-3, 5-21, 20, 29-43 by E. P:juions ; 4 by G. B Simpson ; 22-25,27,28 by 1{. F. WniTFIEbD ) 
Genus DIELA8MA, King. 
Page 293. 
Dielasma turgiua, Hull. 
Fig'S. 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 highly ventricose valves. 
St. Louis grouji. Washington county, Indiana. 
Figs. 5, 6. 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 1-$. 
Chester group. Spencer county, Indiana. 
Diei.asma Burlingtonensis, ^Vhito. 
Figs. 9-11 Dorsal, profile and ventral views of a small shell. 
Chert of the Burlington limestone. Louisiana,, Missouri. 
Dielasma Formosa, Hull. 
Figs. 12, 13. Profile and dorsal views of a small internal cast. 
Fig. 14. Profile of a shell of about the same size, but with more gibbous valves. 
Fig. 15. Doi'sal view of an internal cast; showing that in these small shells the muscular platform of the 
brachial valve is uot clearly defined. 
St. Louis group. 
Fig. 16. A cast of the cardinal poi-tion of the pedicle-\ alve, enlarged to show the cavity left by the enfolded 
margin of the pedicle-passage, the dental lamellae and deltidial plates. X 2. 
Fig. 17. An internal cast of the brachial valve ; showing the impression left by the base of the muscular 
platform, and the genital markings about the muscular ai-ea. 
Figs. 18, 19. Profile and dor.sal views of a specimen of medium size. 
St. Louis group. 
Fig. 20. Dorsal view of a large individual I'etaining the shell. 
Fig. 21. Dorsal view of a specimen cut to expose the loop. 
Figs. 22, 23. Ventral and dorsal views of the looj) 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 base of the muscular platform, and 
divergent, probably vascular impressions over the adjoining surface. 
Figs 25, 26. Profile and dorsal views of a characteristic and somewhat gibbous example. 
St. Louis group. 
Dielasma Rowleyi, Wortlien. 
Figs. 27, 28. Profile and dorsal views of an internal cast, referi-ed with hesitation to this species ; showing 
the muscular platform of the brachial valve, and the cavities of the dental lamellae. 
Choteau limestone. Gh’aydo7i Spi'ings, MissouH. 
Dielasma bovidens, Morton 
Figs. 29, 30. Dorsal and profile views of a rather gibbous specimen ; showing the contour of the valves and 
the oblique foramen The concenti-ic surface lines a ppear to be to some extent color-markings, 
and not infrequently faint traces of a radial coloration are discernible in the shells. This 
specimen is of about the average size of the species as it occurs at this locality. 
Upper Carbonifei'ous. Kansas City,^Missouri. 
