KIRKBYIDAE 



49 



about midway between ends; second keel 

 located well downward in lateral view 

 appears almost to coincide with free margin ; 

 narrow shield-like appearance produced by 

 carina around cardinal area pronounced ; 

 inner carinae parallel to middle one, ter- 

 minate along line extending horizontally 

 through pit; pit oval, directly beneath node 

 but slightly flattened at top. 



Length, 0.93 mm ; height, 0.60 mm ; 

 thickness, 0.61 mm. 



Golconda formation, locality 17, rare; 

 Glen Dean formation, locality 11, abundant. 



A. carinatus on first examination appears 

 to be identical with A. centronotus (Ulrich 

 and Bassler), but the following differences 

 may be noted : the form ratio of the Chester 

 species is 1.5 while the average of the many 

 published figures of A. centronotus is more 

 than 1.7; the pit is more centrally located 

 and much larger ; and the central keel is 

 much closer to the free margins than in the 

 younger species. The form described from 

 the Golconda by Groneis and Gale is pro- 

 bably a crushed specimen. 



parallel to the hinge line; reticulations of 

 medium size, more or less without orderly 

 arrangement. 



Length, 0. 69 mm; height, 0.40 m. 



Kinkaid formation, locality 3, common. 



Amphissites rugosus Girty 

 Plate 9, figures 1-3 



Amphissites rugosus Girty, 1910, Ann. New York 



Acad. Sci., vol. 20, p. 236, Fayetteville shale. 



Roundy, 1926, U. S. Geol. Survey, Prof. 



Paper 146, p. 7, pi. 1, figs, la-c, Barnett shale. 

 Amphissites ivewveri Roth, 1929, Wagner Free 



Ins. Sci., vol. 1, pp. 9, 36, 39, pi. 2, figs. 



lla-c. 



Length, 0.80 mm; height, 0.46; thickness, 

 0.45 mm. 



Kinkaid formation, locality 3, rare. 



The Kinkaid specimen, although smaller 

 than the holotype, has the same form ratio, 

 1.7. The arrangement and number of 

 carina, and character of reticulations also 

 correspond so that this form has been con- 

 fidently identified with Girty's species. 



Amphissites exiguus Cooper, n. sp. 

 Plate 9, figures 13-15 



Carapace small, asymmetrical in lateral 

 view, anterior end lowest; inner carina 

 prominently developed as broad, smooth 

 flange, not parallel to outer carina; node 

 very small, central; pit small, almost indis- 

 tinguishable ; anterior shoulder broad, not 

 keel-like ; reticulations fine and irregularly 

 arranged ; hinge line straight and depressed. 



Length, 0.50 mm; height, 0.30 mm; 

 thickness, 0.29 mm. 



Kinkaid formation, locality 3, rare. 



This species is similar to A. carinatus 

 n. sp. in dorsal area, but differs in possess- 

 ing a higher inner carina, a much smaller 

 central node, and a broad anterior shoulder 

 as contrasted to the antero-dorsal carina of 

 the latter species. 



Amphissites quadratus Cooper, n. sp. 

 Plate 9, figure 4 

 Carapace elongate, somewhat rectangular, 

 small round central node directly above 

 deep oval pit ; outer carina smooth, pro- 

 minent, parallel to free margin ; inner carina 

 poorly developed at each end, subparallel to 

 outer one; inner ridges faint, joining ridge 



Genus Ectodemites Cooper, n. gen. . 



Amphissites, in part, of authors. 



Kirkbyidae with regularly convex, or in- 

 flated, ovate carapace, marked by one or 

 more false keels but without well-defined 

 nodes ; regularity of curvature often inter- 

 rupted by slight swelling near central por- 

 tion above pit. 



Genotype. — Ectodemites primus n. sp. 



This genus differs from Kni^htina in the 

 absence of the prominent kirkbyan shoulder. 

 The slight central swelling of Ectodemites 

 should not be confused with the well defined 

 central node of Amphissites and Polytylites. 



Ectodemites bicarinatus 



(Croneis and Thurman) 



Plate 9, figures 50-51 



Ajnphissites bicarinatus Croneis and Thurman, 

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

 vol. 33, p. 311, pi. 7, figs. 10-12, Kinkaid 

 formation. 



Length, 0.91 mm; height, 0.55 mm; 

 thickness, 0.55 mm. 



Vienna formation, locality 10, common; 

 Menard formation, locality 7, rare; Kinkaid 

 formation, locality 28, depth 628-33 feet, 

 common. 



