BEYRICHIIDAE 



37 



smaller than right due to prominent over- 

 lap ; posterior end asymmetrically rounded, 

 due to flattening of curvature of postero- 

 ventral portion of left valve ; greatest 

 length above middle ; antero-ventral margin 

 of left valve slightly upturned ; in dorsal 

 view hinge line sinuous, offset at articula- 

 tion prominent ; greatest thickness posterior ; 

 greatest height central. 



Length, 0.98 mm ; height, 0.62 mm ; 

 thickness, 0.42 mm. 



Golconda formation, locality 22, rare. 



Cavellina ovatiformis (Ulrich) 

 Plate 5, figures 45-48 



Cytherella ovatifortnis Ulrich, 1891, Jour. Cin- 

 cinnati Soc. Nat. Hist., vol. 13, p. 209, pi. 17, 



figs. 3, 4a-c, Chester series. Batalina, 1924, 



Bull. Com. Geol., vol. 43, no. 10, pp. 1324, 

 1335, pi. 22, fig. 7, pi. 23, figs. 12-14, Lower 

 Carboniferous of Russia. 



Cavellina mediocris Croneis and Thurman, 1938, 

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

 p. 327, pi. 7, fig. 17, Kinkaid formation. 



Cavellina oralis Croneis and Funkhouser, idem, 

 p. 358, pi. 10, figs. 9, 10, Clore formation. 



Length, 1.03 mm; height, 0.69 mm; 

 thickness, 0.49 mm. 



Paint Creek formation, locality 24, 

 abundant; Vienna formation, locality 10, 

 common ; Menard formation, locality 32, 

 rare; Kinkaid formation, locality 5, com- 

 mon; Fayetteville shale, locality 31, 

 abundant. 



Cavellina parva Cooper, n. sp. 

 Plate 5, figures 39-40 



Carapace small, subelliptical, smooth ; 

 overlap greatest on dorsum and venter; 

 posterior end slightly less regularly curved 

 than anterior ; greatest length slightly above 

 center; greatest height slightly forward of 

 center, greatest thickness back of center ; 

 posterior end somewhat upturned ; hinge 

 line sinuous, due to increase of overlap in 

 anterior half. 



Length, 0.78 mm; height, 0.49 mm; 

 thickness, 0.33 mm. 



Vienna formation, locality 10, common. 



The position of the greatest height, just 

 forward of the middle, serves to distinguish 

 this species which is somewhat intermediate 

 between Cavellina and Paracavellina; how- 

 ever, it does not possess the posterior ridge 

 of the latter genus. 



Genus Paracavellina Cooper, n. gen. 



Carapace cytherelloid in outline; overlap 

 right over left around entire margin ; dorsal 

 and ventral margins arched to form greater 

 overlap at these points; curvature of valves 

 interrupted at each end by ridge close to 

 and parallel with margins resulting in 

 furrow just inside the ridge; surface smooth 

 to granulose or minutely pitted. 



Genotype. — P. elliptica n. sp. 



This genus is distinguished from Cavel- 

 lina by the ventral arch and terminal ridges ; 

 from Birdsallella and Cavellinella by the 

 presence of the anterior ridge and the loca- 

 tion of the posterior ridge much closer to 

 the margin. 



Paracavellina elliptica Cooper, n. sp. 

 Plate 6, figures 5-6 



Carapace elliptical, like Cavellina in out- 

 line, greatest height and length central; 

 overlap around entire margin ; regular 

 convexity of right valve interrupted at each 

 end by abrupt swelling, forming more or 

 less prominent ridge parallel to terminal 

 margins ; ridge extends farther around 

 venter than around dorsum, matched on the 

 left valve by a slight swelling that is much 

 less noticeable on the right valve; width 

 of left valve increased by regular increase 

 in amount of overlap from each end toward 

 center; greatest thickness in posterior 

 quarter. 



Length, 1.06 mm; height, 0.67 mm; 

 thickness, 0.48 mm. 



Golconda formation, locality 17, rare. 



Paracavellina opima Cooper, n. sp. 

 Plate 6, figures 34-35 



Carapace short, ovate, tumid ; terminal 

 ridges somewhat prominent; ends broadly 

 curved ; dorsum arched, venter almost 

 straight; greatest overlap along venter; 

 hinge straight ; greatest length and height 

 central ; greatest thickness posterior ; sur- 

 face smooth. 



Length, 0.68 mm ; height, 0.49 mm ; 

 thickness, 0.33 mm. 



Paint Creek formation locality 24, rare. 



Paracavellina ovata Cooper, n. sp. 



Plate 6, figures 3-4 



Carapace ovate; dorsum strongly arched, 

 venter almost straight ; terminal ridges low, 



