164 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxx. 



10. Another left valve having the anterior swelling characterizing the 



variety but <liffering from other specimens in the ol)solescence of the 

 anterior one of the two median tubercles. 



11. Ventral view of original of Hg. 10, showing the inflation of the anterior 



end. 

 Cottonwood shales, 2 miles east of Cottonwood Falls, Kansas. 



Fig. 12. Ci/there f luiworlhi, new species. 



Fi<i. 12. View of left valve showing the ventral wing-like process, the tubercles 

 and surface markings characterizing this minute species. 

 Cottonwood shales, 2 miles east of Cottonwood Falls, Kansas. 



Fuis. 13-15. Kirkbyci pingdiK, new species. 



Fn;. 13. Left side of an example retaining both valves. 

 14. Posterior view of same specimen, 

 lo. Ventral view of same. 

 Cottonwood shales, 2 miles east of Cottonwood Falls, Kansas. 



Fuis. l(i, 17. Kirkhijn rciilronotd, new species. 



Fi(i. It). Right valve of a fully developed anil well-marked example showing the 

 concentric arrangement of the ridges and reticulate ornament, and 

 the strongly developed dorsal ridge. 

 17. Anterior view of same showing the thick dorsal and ventral edges. 

 Cottonwood shales, 2 miles east of Cottonwood Falls, Kansas. 



Fk;. is. Bei/rifJiielld (/n'(j<(ri<t, new species. 



Fi<i. 18. Left valve of an average old example of this rather variable species, in 

 young valves the o])scurely defined ventral flange is much narrower 

 or is wanting, and in such ca.-^es the denticulated contact edge beneath 

 may be visible in a side view. 

 Coal Measures, Kansas City, Missouri. 



Fi<is. 19, 20. Balrdla heedei, new species. 



Fi(is. 19,20. Right side and ventral views of a comi)letc example. End view 

 about as in figure 22. 

 Cottonwood shales, 2 miles east of Cottonwood Falls, Kansas. 



F^uis. 21, 22. Bitirdia heedei ahrnpta, new variety. 



Fi<is. 21,22. Views of right side and posterior end showing the more abruptly 

 tapering posterior i)ortion tlnit distinguishes tlie variety. F^dge view 

 about as in figure 20. 

 Cottonwood shales, 2 miles east of Cottonwood Falls, Kansas. 



F^ics. 23-20. Ci/pridiiKi nidionda, new species. 



Fio. 23. Left valve, with the test somewhat exfoliated, so as to show tlu> mus- 

 cular scar, X 0. 



24. Dorsal outline of same, sliowing postero-canlinal projection. 



25. Posterior view in outline of same, likewise showing the post-cardinal 



jirojection of margin sujiposed to indicate a limited overlap of valves. 

 20. Riglit valve drawn from a gutta-percha S(|ueeze, X 0, showing slight 

 difference in outline of post-carduial portion when c'oinj>anMl with 

 left valve. 

 Lawrence shaU's, Lawn-ncc, Kansas. 



