EXPLANATION OF PLATES 



U.S.N.M. = United States National Museum 



U.M.M.P. = University of Michigan Museum of Paleontology 



U.S.G.S. = United States Geological Survey 



Plate 1 



Lopha luguhris (Conrad) 



Fig. \. Lateral view (Xl) of a left valve with reverse curvature; a hypotype 



from a calcarenite bed between typical Austin Chalk and Eagle Ford Shale 



(locality 16, U.S.G.S. loc. 7579) ; U.S.N.M. 132154. 

 Fig. 2. Lateral view of a typical left valve (Xl) ; Stanton's hypotype from 



Mancos, Colo, (locality 4, U.S.G.S. 833), the original of his plate 4, 



figure 3 (1893) ; U.S.N.M. 22859b. 

 Fig. 3. Lateral view (X2) of a left valve with abnormally small attachment 



area; a hypotype (locality 38) ; U.S.N.M. 132155. 

 Fig. 4. Lateral view (Xl) of a typical left valve, the lectotsnpe; the original 



of Conrad's (1857) plate 10, figure 5b, (locality 30, east of Red River, 



Santa Fe Road, N. Mex.) ; U.S.N.M. 9822. 

 Fig. 5. Lateral view (X2) of a typical left valve; a hypotype from the 



upper Eagle Ford Shale of Texas (locality 15, U.S.G.S. 7539) ; U.S.N.M. 



132156. 

 Fig. 6. Lateral view (X2) of a left valve with well-developed reverse curva- 

 ture of the exogyroid beaks and umbo; a hypotype from Huerfano Park, 



Colo, (locality 34) in the Juana Lopez Member (Carlile Shale) ; 



U.M.M.P. 43472. 

 Fig. 7. Lateral view (X2) of a typical left valve; a hypotype from the zone 



of Prionocyclus wyomingensis wyomingensis, near Casa Salazar, N. Mex. 



(locality 17, U.S.G.S. 7993) ; U.S.N.M. 132157. 

 Fig. 8. Lateral view (X2) of an unusually erect left valve; a hypotype from 



the upper 3 feet of the Eagle Ford Shale, Texas (locality 48, U.S.G.S. 



11732) ; U.S.N.M. 132158. 

 Fig. 9. Lateral view (X2) of a left valve with a large, flat attachment scar 



and somewhat restricted plicae ; a hypotype from the Juana Lopez Member, 



Huerfano Park, Colo, (locality 34) ; U.M.M.P. 43464. 

 Fig. 10. Lateral view of a left valve (X2) ; a hypotype from the Juana 



Lopez Member, Huerfano Park, Colo. (locality 34) ; U.M.M.P. 43472. 

 Fig. 11. Lateral view (X2) of a distorted left valve with plicae limited to the 



margins; a hypotype from Mancos, Colo, (locality 4, U.S.G.S. 833); 



U.S.N.M. 22210a. 

 Fig. 12. Lateral view (X2) of a nearly smooth left valve with only faint 



marginal plicae; a hypotype from the Juana Lopez Member, Huerfano 



Park, Colo, (locality 34) ; U.M.M.P. 43465. 

 Fig. 13. Lateral view (X2) of an erect left valve with a large scar and 



relatively few, restricted, marginal plicae; a hypotype from the Juana 



Lopez Member, Huerfano Park, Colo, (locality 36) ; U.M.M.P. 43476. 



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