26 



CHESTER OSTRACODES OF ILLINOIS 



Bairdia granireticulata Harlton 

 Plate 1, figures 17-20 

 Bairdia giumircticulata Harlton, 1929, Am. Jour. 

 Sci., ser. 5, vol. 18, p. 267, pi. 2, figs. 10 a, b, 

 Fayetteville shale. 

 Carapace tumid; dorsum broadly arched, 

 with ahnost equal slope toward each end, 

 venter curved; overlap around entire mar- 

 gin prominent except at anterior portion; 

 antero-dorsal intersection slightly greater 

 than 90°; postero-dorsal slope about 50°; 

 posterior end short, sharp, slightly upturned ; 

 surface granulose. 



Length, 1.17 mm; height, 0.53 mm; 

 thickness, 0.43 mm. 



Golconda formation, locality 17, com- 

 mon; Paint Creek formation, locality 18, 

 common. 



Bairdia impendere Cooper, n. sp. 

 Plate 2, figures 7-8 



Carapace short and high with strong 

 overlap around the entire margin, parti- 

 cularly on the postero-dorsal portion; dor- 

 sum strongly curved, venter almost straight ; 

 hinge and articulation form broad curve in 

 dorsal view; terminal projection somewhat 

 long and very low, one-fourth the height of 

 the shell above the venter; greatest height 

 forward of center, greatest length just be- 

 low center; postero-dorsal slope about 55°; 

 surface smooth. 



Length, 1.23 mm; height, 0.80 mm; 

 thickness, 0.50 mm. 



Renault formation, locality 14, rare. 



Bairdia insolens Cooper, n. sp. 

 Plate 2, figures 1-2 



Carapace elongate, dorsum curved, ven- 

 ter straight ; antero-ventral margin meeting 

 upper and lower margins at an angle ; over- 

 lap prominent around entire margin, includ- 

 ing hinge; posterior projection short and 

 low; postero-dorsal slope about 55°; sur- 

 face smooth. 



Length, 1.44 mm; height, 0.73 mm; 

 thickness, 0.50 mm. 



Renault formation, locality 12, common. 



This form may be distinguished by its 

 complete overlap and the unusual curvature 

 of the anterior end. 



Bairdia sinuosa Cooper, n. sp. 

 Plate 2, figures 11-12 

 Carapace ovate, tumid; left valve over- 

 laps right except at apex of dorsum and at 



posterior ventral corner; in dorsal view 

 hinge and overlap form smooth, sinuous 

 curve; dorsum slightly curved, right valve 

 projecting slightly above hinge; postero- 

 dorsal slope about 50° ; ventral margin 

 straight; anterior margin curved; greatest 

 height at center, greatest length slightly 

 above center; posterior projection short, 

 located below center line; surface smooth. 



Length, 1.0 mm; height, 0.51 mm; 

 thickness, 0.40 mm. 



Clore formation, locality 52, common; 

 Kinkaid formation, locality 5, abundant. 



B. sinuosa might be confused with B. 

 cestriensis Ulrich but it does not possess the 

 depressed hinge line of the latter species. 



Bairdia cf . subelongata Jones and Kirkby 



Plate 2, figures 3-4 

 Bairdia subelongata Jones and Kirkby, 1879, 



Quart. Jour., Geol. Soc. London, vol. 35, p. 



573, pi. 30, figs. 1-11, 16, Carboniferous of 



Great Britain. 



Carapace thin, rounded anteriorly, 

 slender and tapering posteriorly; postero- 

 dorsal slope low (ca. 35°), venter gently 

 convex; overlap not conspicuous. 



Length, 1.30 mm; height, 0.52 mm; 

 thickness, 0.40 mm. 



Golconda formation, locality 19, common. 



Bairdia subtila Cooper, n. sp. 

 Plate 2, figures 5-6 



Carapace wide, dorsum acutely arched, 

 especially posteriorly; postero-dorsal slope 

 50°, venter concave and strongly overlap- 

 ped ; Intersection of anterior and dorsal 

 margins about 90 ° ; greatest height central ; 

 greatest thickness In middle of posterior 

 half ; posterior projection very poorly de- 

 veloped. 



Length, 1.27 mm; height, 0.53 mm; 

 thickness, 0.37 mm. 



Kinkaid formation, locality 3, abundant. 



This species is very similar to B. nasuta 

 Morey, but differs In Its concave venter and 

 lack of the symmetrical lens-like dorsal out- 

 line. 



Genus Bairdiolites Croneis and Gale 

 Bairdiolites brevirostris 

 Cronels and Thurman 

 Plate 2, figures 15-16 

 Bairdiolites brevirostris Croneis and Thurman, 

 1938, Bull. Denison Univ., Jour. Sci. Lab., 

 vol. 33, p. 326, pi. 7, fig. 20, Kinkaid forma- 

 tion. 



