BARIDIIDAE 



33 



Length 0.62 mm; height, 0.37 mm; 

 thickness, 0,32 mm. 



Renault formation, locality 9, abundant; 

 Paint Creek formation, locality 24. rare. 



/. prima may be distinguished from 7. 

 lata n. sp. by its elongate anterior end, 

 greater relative length, and somewhat 

 smaller ovate posterior depression. 



Incisurella lata Cooper, n. sp. 

 Plate 4, figures 21-22 



Carapace short, subovate, thick, ends 

 rounded ; ventral margin slightly convex ; 

 posterior and anterior dorsal slopes almost 

 equal, greatest height nearly central ; over- 

 lap moderate on ends, greater on ventral 

 margin ; ovate depressed area, shallow, sub- 

 central, in center of curve around posterior 

 quarter as seen in dorsal view ; depression 

 bordered by low, very narrow rim ; surface 

 smooth. 



Length, 0.60 mm; height, 0.37 mm; 

 thickness, 0.28 mm. 



Renault formation, locality 25, rare; 

 Paint Creek formation, locality 24, com- 

 mon. 



Genus Microcheilinella Geis 



MiCROCHEILINELLA CORDATA 



Cooper, n. sp. 

 Plate 4, figures 23-24 



Carapace ovate, very thick, ends rounded, 

 left valve overlaps right along venter and 

 anterior end; posterior articulation depress- 

 ed, producing decided heart-shaped outline 

 in ventral view; hinge curved and slightly 

 channeled ; dorsum arched ; venter straight ; 

 greatest thickness posterior ; surface smooth. 



Length, 0.45 mm ; height, 0.22 mm ; 

 thickness, 0.60 mm. 



Kinkaid formation, locality 3, rare. 



Microcheilinella? exilis Cooper, n. sp. 

 Plate 4, figures 45-46 



Carapace elongate, slender; ends round- 

 ed, posterior slightly more acute; dorsum 

 straight, venter slightly convex; greatest 

 length about central; greatest height and 

 thickness back of middle; dorsal area some- 

 what flattened ; overlap around free margin 

 inconspicuous; hinge straight, surface 

 smooth. 



Length, 0.53 mm; height, 0.18 mm; 

 thickness, 0.15 mm. 



Renault formation, locality 9, common. 



The generic affinities of this small slender 

 form are somewhat obscure and it is being 

 provisionally placed under Microcheilinella 

 because of the flattened dorsal area and the 

 slightly more acuminate posterior end. 



Microcheilinella obesa Cooper, n. sp. 



Plate 4, figures 35-38 



Carapace ovate, thick; left valve larger 

 and thicker than right ; prominent overlap 

 around free margin; ends rounded, dorsum 

 arched, venter straight; hinge curved, 

 channeled ; greatest length central ; greatest 

 height and thickness posterior ; surface 

 smooth. 



Length, 0.58 mm; height, 0.30 mm; 

 thickness, 0.37 mm. 



Paint Creek formation, locality 21, rare; 

 Menard formation, locality 28, depth 838- 

 44 feet, rare ; Kinkaid formation, locality 

 28, rare. 



This species differs from M. cordata 

 n. sp. in that it does not possess the indented 

 posterior articulation which gives the latter 

 species its heart-shaped outline. It also 

 appears to be very close to M. subcorbuloides 

 (Jones and Kirkby) and is about the same 

 size as a form from the Barnett shale ten- 

 tatively referred to the latter species by 

 Roundy (1926, p. 8). 



Microcheilinella tumida Cooper, n. sp. 

 Plate 4, figures 47-49 



Carapace ovate, tumid ; ends rounded, 

 posterior slightly more acute than anterior; 

 venter straight; left valve larger, overlaps 

 around entire free margins; hinge line 

 depressed, sinuous; greatest length and 

 height central ; greatest thickness posterior ; 

 surface smooth. 



Length, 0.52 mm; height, 0.25 mm; 

 thickness, 0.28 mm. 



Paint Creek formation, locality 2, rare; 

 Golconda formation, locality 17, rare; 

 Vienna formation, locality 36, rare; Kin- 

 kaid formation, locality 3, rare. 



Genus Seminolites Coryell 



Seminolites ovalis Cooper, n, sp. 



Plate 4, figures 32-34 



Carapace ovate, almost elliptical in lateral 

 view, ends rounded, dorsum curved, venter 

 slightly convex; overlap pronounced along 

 posterior and ventral margms, slight along 



