BARIDIIDAE 



31 



also shows this slope. The Golconda form 

 in addition to agreeing very closely with the 

 British Carboniferous limestone specimen 

 possesses a well-defined channel along the 

 line of articulation on this slope. 



Healdia elliptica Cooper, n. sp. 

 Plate 3, figures 43-45 



Carapace elongate, subsymmetrical in out- 

 line; anterior end rounded; venter slightly 

 less convex than dorsum; antero- and 

 postero-dorsal slopes almost equal ; posterior 

 transverse ridge, located well back from 

 end, vertical, slightly concave forward ; each 

 end terminated by knob or short spine ; dor- 

 sal outline lens-shaped; greatest thickness 

 back of middle; overlap prominent along 

 venter and anterior margin. 



Length, 0.58 mm; height, 0.33 mm; 

 thickness, 0.25 mm. 



Golconda formation, locality 19, 

 common. 



Healdia menisca Cooper, n. sp. 

 Plate 4, figures 3-5 



Carapace ovate, ends rounded, dorsum 

 arched, venter almost straight; transverse 

 rib, located fairly close to posterior end, 

 strongly curved, merging into upper and 

 lower margins in posterior quarter ; greatest 

 thickness just in front of rib in center of 

 posterior half; greatest height almost 

 central; articulation channelled on the 

 postero-dorsal slope and end; surface 

 smooth; overlap moderate along venter and 

 antero-dorsal slope, slight on anterior end. 



Length, 0.58 mm; height, 0.35 mm; 

 thickness, 0.28 mm. 



Paint Creek formation, locality 24, depth 

 2454-56 feet, abundant. 



This species is characterized by the chan- 

 nelled posterior and the lack of nodes or 

 spines. A reversal of overlap of this species 

 would produce a form similar to Cavellin- 

 ella. H, menisca does not possess the postero- 

 dorsal shoulder of Aurigerites. 



Healdia exilis Cooper, n. sp. 

 Plate 3, figures 52-54 



Carapace ovate, high and thin; dorsum 

 arched, postero-dorsal slope somewhat flat- 

 tened; low rib curved in wide arc, its ends 

 merging with surface of shell near apex of 

 arched dorsum, venter near posterior quart- 

 er ; overlap prominent along venter, moder- 

 ate on ends; greatest height central, greatest 

 width through posterior quarter. 



Length, 0.60 mm; height 0.38 mm; 

 thickness, 0.26 mm. 



Vienna formation, locality 10, abundant. 



Healdia cf. fayettevillensis Harlton 



Plate 3, figures 50-51 



Healdia fayette'villensis Harlton, 1929, Am. Jour. 

 Sci., ser. 5, vol. 18, p. 263, pi. 2, figs. 2a-c, 

 Fayetteville shale. 



Length, 0.50 mm; height, 0.31 mm; 

 thickness, 0.24 mm. 



Menard formation, locality 7, rare ; Clore 

 formation, locality 4, common. 



The Clore specimens seem to be somewhat 

 longer than the Fayetteville forms, although 

 the two specimens illustrated by Harlton 

 vary as much as 13 per cent in form ratio. 

 The Chester form agrees very closely in 

 general outline and in the development of 

 the posterior end. 



Healdia minuta Cooper, n. sp. 

 Plate 4, figures 6-7 



Carapace small, short; ends rounded; 

 dorsum slightly arched, venter convex; rib 

 straight and inclined slightly backward ; 

 postero-dorsal slope somewhat flattened ; 

 overlap not pronounced; greatest height 

 and thickness central. 



Length, 0.48 mm; height, 0.40 mm; 

 thickness, 0.20 mm. 



Paint Creek formation, locality 24, 

 common. 



Healdia mucronata Cooper, n. sp. 

 Plate 4, figures 8-10 



Carapace ovate, anterior end pointed, 

 posterior bluntly rounded, dorsum and 

 venter curved ; wedge-shaped in dorsal 

 view; transverse ridge almost straight, ver- 

 tical, close to posterior end. Ends of the 

 ridges curve back to meet dorsal and ven- 

 tral margins near the posterior quarter, 

 giving postero-dorsal area triangular aspect ; 

 articulation on postero-dorsal slope chan- 

 nelled ; overlap not conspicuous. 



Length, 0.42 mm; height, 0.27 mm; 

 thickness, 0.22 mm. 



Golconda formation, locality 19, rare. 



This species may be distinguished by its 

 pointed anterior end and by the abrupt 



