NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 9I 



Fig. 18. Lateral view of a large left valve, characteristic of the subspecies ; 



a paratype from the Mancos Shale at Carthage, N. Mex. (locality 64, 



U.S.G.S. 3297) ; U.S.N.M. 132274. 

 Fig. 19. Lateral view of an unusually high left valve, otherwise characteristic 



of the subspecies; a paratype from the Mancos Shale at Carthage, N. 



Mex. (locality 65, U.S.G.S. 5303) ; U.S.N.M. 132275. 



Plate 8 

 Lopha hellaplicata novamexicana Kauff man, new subspecies 



Fig. 1-3. Anterior views of left valves illustrating the range in convexity, the 

 great convexity of the umbonal region, and the dorsal position of the high 

 point of the valve. All specimens from the Mancos Shale of New Mexico, 

 zone of Collignoniceras hyatti. 1, U.S.N.M. 132282, from locality 66. 

 2, U.S.N.M. 132271, from locality 64. 3, U.S.N.M. 132276, from locality 

 66. All figures Xl- 



Fig. 4, Lateral view (Xl) of a left valve, characteristic of the subspecies 

 except for fainter plicae; paratype from locality 66, U.S.G.S. D2042, 

 Mancos Shale, zone of Collignoniceras hyatti, Socorro County, N. Mex. 

 U.S.N.M. 132277. 



Fig. 5. Lateral view (Xl) of a left valve with large vertical attachment 

 scar and unusually fine plicae; paratype from the Mancos Shale, zone of 

 Collignoniceras hyatti, Socorro County, N. Mex. (locality 66, U.S.G.S. 

 D2042) ; U.S.N.M. 132278. 



Fig. 6. Lateral view (Xl) of a large left valve transitional with L. hella- 

 plicata hellaplicata in development of plicae and auricular sulci, but retain- 

 ing characteristic shell form of the subspecies; a paratype from the 

 Mancos Shale, zone of C. hyatti, Socorro County, N. Mex. (locality 66, 

 U.S.G.S. D2042) ; U.S.N.M. 132279. 



Fig. 7. Lateral view of a large left valve (Xl) characteristic of the sub- 

 species; a paratype from the zone of C. hyatti, Mancos Shale, Socorro 

 County, N. Mex. (locality 66, U.S.G.S. D2042) ; U.S.N.M. 132280. 



Fig. 8. Lateral view (Xl) of a typical left valve with worn plicae; a paratype 

 from the zone of C. hyatti, Mancos Shale, Socorro County, N. Mex. 

 (locality 66, U.S.G.S. D2042) ; U.S.N.M. 132281. 



Fig. 9. Lateral view (Xl) of a typical large, adult left valve; a paratype 

 from the zone of C hyatti, Mancos Shale, Socorro County, N. Mex. 

 (locality 66, U.S.G.S. D2042) ; U.S.N.M. 132282. 



Lopha hellaplicata hellaplicata (Shumard) 



Fig. 10. Thin section (X4) through the umbo and cardinal area of a large 

 left valve; section parallel to the hinge line. Note major layers in sub- 

 nacreous layer, and fine crystalline calcite sheets within them. Fine layers 

 inclined to plane of major layers over umbo, parallel to this plane 

 laterally; a hypotype from the upper Eagle Ford Shale, Dallas County, 

 Tex. (locality 15, U.S.G.S. 7539) ; U.S.N.M. 132283. 



Fig. 11. Thin section (X4) taken along the median plica, showing the struc- 

 ture of the subnacreous shell layer, the "hingement" of the valves, position 



