52 



CHESTER OSTRACODES OF ILLINOIS 



This species may be distinguished by the 

 subcentral position of the central node, the 

 upper margin of which almost reaches the 

 hinge line, and the unusually large flat area 

 developed in front of the anterior shoulder. 



POLYTYLITES BIFORATUS 



(Croneis and Thurman) 

 Plate 10, figure 23 



Amphissites hiforatus Croneis and Thurman, 

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

 vol. 33, p. 312, pi. 8, figure 9, Kinkaid for- 

 mation. 



Length, 0.87 mm ; height, 0.46 mm. 



Golconda formation, locality 8, common. 



POLYTYLITES BRADFIELDI 



(Croneis and Funkhouser) 

 Plate 10, figures 24-26 



Amphissites hradfieldi (not A. rothi) Croneis 



and Funkhouser, 1938, Bull. Denison Univ.. 



Jour. Sci. Lab., vol. 33, p. 346, pi. 10, fig. 15, 



Clore formation. 

 Amphissites lineatus Croneis and Bristol, 1939, 



idem. vol. 34, p. 83, pi. 4, figs. 1, 2, Menard 



formation. 



Length, 1.0 mm; height, 0.58 mm; 

 thickness, 0.55 mm. 



Renault formation, locality 9, common ; 

 Vienna formation, locality 10, abundant; 

 Menard formation, locality 30, common ; 

 Clore formation, locality 4, abundant ; Kin- 

 kaid formation, locality 5, common. 



POLYTYLITES CONCAVUS 



(Croneis and Bristol) 



Amphissites conca'vus Croneis and Bristol, 1939, 

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

 p. 79, pi. 4, figs. 8, 9, Menard formation. 



POLYTYLITES CRASSus Cooper, n. sp. 

 Plate 10, figures 15-17 



Carapace small, but very thick, highest 

 on posterior end ; central node prominent ; 

 anterior shoulder high, but of smaller 

 diameter than the node; posterior swelling 

 absent; pit small and indistinct; inner keel 

 distinct, parallel to outer one only in 

 postero-ventral region ; reticulations fine. 



Length, 0.40 mm;, height, 0.24 mm; 

 thickness, 0.27 mm. 



Kinkaid formation, locality 3, common. 



POLYTYLITES DIRECTUS Cooper, n. sp. 

 Plate 10, figure 43 



Carapace flat, with three nodes and pro- 

 minent inner keel rising abruptly from 



surface ; anterior and central nodes dis- 

 tinctly elongate vertically posterior node al- 

 most circular ; inner keel unusually high, 

 parallel to free margin, except at posterior 

 extremity; inner side marked by single row 

 of pits elongated radially; in dorsal view 

 space between the two carinae occupied by 

 at least five rows of reticulae; pit small, 

 subcircular, slightly forward of ventral end 

 of central node. 



Length, 0.98 mm ; height, 0.53 mm. 



Glen Dean formation, locality 1, rare. 



POLYTYLITES DIVERSUS Cooper, n. sp. 

 Plate 10, figure 4 



Carapace small, thicker but much lower 

 on anterior end ; greatest height through 

 posterior end of hinge ; anterior shoulder and 

 central node poorly developed; pit slightly 

 forward of and below center of shell ; 

 surface marked by comparatively coarse re- 

 ticulations; inner keel parallel to outer one 

 along ventral margin only, diverging at 

 either end. 



Length, 0.43 mm ; height, 0.27 mm. 



Vienna formation, locality 10, rare. 



POLYTYLITES ELONGATUS 



(Croneis and Bristol) 



Plate 10, figure 44 



Amphissites elongatus Croneis and Bristol, 1939, 

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

 p. 81, pi. 4, fig. 10, Menard formation. 



Length, 0.97 mm; height, 0.56 mm, 

 Kinkaid formation, locality 5, common, 



POLYTYLITES FOSSILIS 



(Croneis and Thurman) 



Plate 10, figures 51-52 



Arnphissites fossilis Croneis and Thurman, 1938, 

 Denison Univ. Bull., Jour. Sci. Lab., vol. 33, 

 p. 312, pi. 8, fig. 18, Kinkaid formation. 



Length, 0.85 mm; height, 0.47 mm. 



Renault formation, locality 9, common; 

 Paint Creek formation, locality 2, rare; 

 Golconda formation, locality 8, common. 



POLYTYLITES GENICULATUS Cooper, n. sp. 

 Plate 10, figures 34-37 



Carapace small, somewhat rectangular in 

 outline, with inner sharp, well-defined 

 carina marking broad curve nowhere paral- 

 lel to outer one ; small, round node rises 

 abruptly (and is relatively high) from 

 shell surface, a little above and behind cen- 



