30 



CHESTER OSTRACODES OF ILLINOIS 



ridge bordered by a punctate sinus is located 

 near the anterior end. None of the Chester 

 specimens have even the faintest anterior 

 ridge, but some do show an abrupt change 

 in the curvature of the shell anteriorly, 

 marked by a row of pits. If this is what 

 Harlton designates as the anterior ridge, the 

 two species referred to above belong in the 

 genus Cribroconcha. In any event, the dev- 

 elopment of the posterior end is so different 

 from the typical Seminolites that these 

 species should not be included in that genus. 



Cribronconcha conspicua (Harlton) 



Seminolites conspicuus Harlton, 1929, Am. Jour. 

 Sci., ser. 5, vol. 18, p. 266, pi. 2, figs. 9a-c, 

 Fayetteville shale. 



Cribroconcha fornicata Cooper, n. sp. 

 Plate 3, figures 34-36 



Carapace ovate in lateral outline, post- 

 erior end round, dorsum arched, venter 

 straight where prominent overlap (left over 

 right) makes ventral margin of right valve 

 slightly concave; anterior end truncates on 

 ventral edge, placing greatest length well 

 above center; greatest height central; post- 

 erior end marked by narrow, slightly curved, 

 vertical rib, concave inward, on the inner 

 side of which is a narrow punctate sinus; 

 overlap moderate along anterior end and 

 venter, less so elsewhere; postero-dorsal 

 slope flattened, with hinge incised. 



Length, 0.48 mm; height, 0.30 mm; 

 thickness, 0.23 mm. 



Paint Creek formation, locality 24, 

 common. 



Genus Healdia Roundy 

 Healdia aequabilis Cooper, n. sp. 



Plate 3, figures 17-19 

 Carapace wide and thick, dorsum highly 

 arched, with prominent posterior slope, 

 venter broadly curved ; ends rounded ; post- 

 erior ribs located well back from end of 

 shell, straight and vertical, terminating in 

 short knob; overlap moderate around en- 

 tire margin except posterior dorsal slope, 

 which is channelled ; greatest height central ; 

 greatest thickness at posterior quarter, just 

 in front of ribs. 



Length, 0.63 mm; height, 0.39 mm; 

 thickness, 0.30 mm. 



Renault formation, locality 25, common ; 

 Paint Creek formation, locality 2, common ; 

 Golconda formation, locality 19, common. 



This form resembles H. simplex Roundy 

 but lacks the abrupt posterior end and has 

 a longer posterior dorsal slope, which is 

 channelled from the apex of the dorsal arch. 



Healdia caneyensis Harlton 



Plate 3, figures 46-49 



Healdia caneyensis Harlton, 1927, Jour. Paleon- 

 tology, vol. 1, p. 208, pi. 33, figs. 2 a-c, upper 

 Caney shale; 1929, Am. Jour. Sci., ser. 5, 

 vol. 18, pp. 261, pi. 1, figs. 9 a-c, Springer 

 shale; 1933, Jour. Paleontology, vol. 7, p. 26, 

 pi. 7, fig. 10, Johns Valley shale. ? Brad- 

 field, 1939, Bull. Am. Paleontology, vol. 22, 

 no. 73, p. 105, pi. 8, fig. 14, Dornick Hills 

 formation. 



Length, 0.57 mm; height, 0.35 mm; 

 thickness," 0.27 mm. 



Glen Dean formation, locality 11, 

 abundant. 



There seems to be considerable variation 

 in the form described as H. caneyensis. The 

 drawing of the dorsal view of the genotype 

 is probably not representative, because the 

 angularity shown is not characteristic of any 

 known Healdia. However, the lateral view 

 of this species shown later by Harlton 

 (1929, pi. 1, fig. 9e) shows the typical 

 dorsal outline. 



Healdia cornigera (Jones and Kirkby) 

 Plate 3, figures 14-16 



Cythere cornigera Jones and Kirkby, 1867, Ms., 



Geol. Soc. Glasgow, vol. 2, p. 223. Vine, 



1884, Proc. Yorkshire Geol. Polyt. Soc, n.s., 

 vol. 8, pp. 223, 239, pi. 12, figs. 9, 9a Car- 

 boniferous of Great Britain, 



Bythocyprisf cornigera Jones and Kirkby, 1886, 

 Ann. Mag. Nat. Hist., ser. 5, vol. 18, p. 251, 

 pi. 6, figs. 8a-c, 9, Carboniferous of Great 

 Britain. 



Healdia cornigera. Latham, 1932, Trans. Roy. Soc. 

 Edinburgh, vol. 57, pt. 2, p. 38, fig. 23, Car- 

 boniferous of Great Britain. 



IVaylandella cornigera. Bassler and Kellett, 1935, 

 Geol. Soc. Am., Spec. Paper 1, p. 491. 



Length, 0.50 mm; height, 0.27 mm; 

 thickness, 0.22 mm. 



Golconda formation, locality 19, rare. 



This species, referred to no less than four 

 different genera, is returned to Healdia 

 because of the work of Latham, who had 

 access to many of Jones and Kirkby's col- 

 lections and to topotype collections from 

 their localities. Waylandella of Coryell and 

 Billings lacks the postero-dorsal slope of 

 Healdia, which the specimen figured by 

 Jones and Kirkby (1886, pi. 6, fig. 8a) 

 surely has. Latham's figure of this species 



