54 



CHESTER OSTRACODES OF ILLINOIS 



Length, 0.89 mm ; height, 0.55 mm. 



Golconda formation, locality 16, com- 

 mon; Glen Dean formation, locality 1, 

 rare; Menard formation, locality 7, com- 

 mon. 



POLYTYLITES TRICOLLINUjS 



(Jones and Kirkby) 

 Plate 11, figures 1-4 



Kirkhya tricollina Jones and Kirkby, 1886, Ann. 

 Mag. Nat. Hist., sen 5, vol. 18, p. 261, pi. 8, 



fig. 19, Carboniferous of England. Ulrich, 



1891, Jour. Cincinnati Soc. Nat. Hist, vol. 13, 

 p. 207, pi. 18, figs. 8a, b, Chester series. 



AmpJtissites tricollina. Roth, 1929, Wagner Free 



Inst. Sci. Pub., vol. 1, p. 3. Bassler and 



Kellett, 1935, Geol. Soc. Am., Spec. Paper 1, 

 p. 155. 



Length, 0.78 mm; height, 0.45 mm; 

 thickness, 0.40 mm. 



Glen Dean formation, locality 1, rare. 



PoLYTYLiTES TRiLOBUS (Croneis and Gale) 



Plate 11, figure 5 



Amp/iissites trilohus Croneis and Gale, 1938, Bull. 

 Denison Univ., Jour. Sci. Lab., vol. 33, p. 271, 

 pi. 5, fig. 5, Golconda formation. 



Length, 1.0 mm; height, 0.55 mm. 



Golconda formation, locality 16, rare. 



PoLYTYLiTES wiLSONi (Croneis andGutke) 



Plate 11, figures 22-23 



Ampliissites ivilsoni Croneis and Gutke, 1939, 

 Denison Univ. Bull., Jour. Sci. Lab., vol. 34, 

 p. 47, pi. 2, figs. 24, 25, Renault formation. 



Length, 0.78 mm; height, 0.44 mm; 

 thickness, 0.40 mm. 



Renault formation, locality 9, common. 



Family Kloedenellidae 

 Ulrich and Bassler 



Genus Chesterella Croneis and Gutke 



Chesterella? incerta Cooper, n. sp. 



Plate 11, figures 28-30 



Carapace subrectangular ; hinge straight, 

 with small tooth at posterior end fitting into 

 corresponding process on right valve ; valves 

 almost equal in size with little or no ap- 

 parent overlap, greatest thickness and least 

 height anterior ; greatest length almost cen- 

 tral or slightly above; ventral lobe rises 

 gradually from posterior, narrowing and 

 terminating abruptly just beneath node in 

 antero-dorsal quarter; posterior node just 

 back of center. 



Length, 0.55 mm; height, 0.30 mm,- 

 thickness, 0.30 mm. 



Renault formation, locality 25, common. 



The orientation of this genus is re- 

 versed from that given by Croneis and Gale 

 because of the backward swing of the valves 

 in lateral view, and by reference to the fam- 

 ily description, the hinge process is located 

 posteriorly. The generic designation of 

 C. incerta and C. fissurata Croneis and Gale 

 have been questioned due to the great 

 similarity of these forms to Jonesina. This 

 is not true for C. exuta Croneis and Gale, 

 which appears to possess characters quite 

 different from those of any other described 

 genus. C. incerta is distinguished from 

 C. fissurata by the narrower anterior end 

 in lateral view. 



Genus Deloia Croneis and Thurman 

 Deloia spinosa Croneis and Bristol 

 Plate 11, figure 18 

 Deloia spinosa Croneis and Bristol, 1939, Bull. 

 Denison Univ., Jour. Sci. Lab., vol. 34, p. 73, 

 pi. 3, fig. 21, Menard formation. 

 Leightonella torta Croneis and Gale, 1938, idem., 

 vol. 33, p. 263, pi. 5, fig. 19, Golconda for- 

 mation. 



Length, 0.95 mm; height, 0.51 mm. 



Renault formation, locality 9, rare ; Glen 

 Dean formation?, locality 1, rare; Vienna 

 formation, locality 10, rare; Menard for- 

 mation, locality 7, rare; Kinkaid formation, 

 locality 3, rare. 



Deloia tumida Cooper, n. sp. 

 Plate 11, figures 13-14 



Carapace ovate, hinge straight ; posterior 

 end rounded, anterior margin meets dorsum 

 in obtuse angle ; valves flat, except at 

 posterior end, where postero-dorsal quarter 

 is abruptly inflated ; free margin coarsely 

 fringed. 



Length, 0.75 mm; height, 0.44 mm; 

 thickness, 0.29 mm. 



Kinkaid formation, locality 3, rare. 



The flatness of the valves is probably ac- 

 centuated by some crushing, but it is be- 

 lieved that the abrupt swelling would still 

 be very prominent in an uninjured specimen. 



Genus Denisonia Croneis and Bristol 

 Denisonia brevicosta Cooper, n. sp. 



Plate 11, figures 40-41 

 Carapace elongate, with slight backward 

 swing, ends rounded ; dorsum straight. 



