NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 83 



Fig. 14. Lateral view (X2) of a left valve with radiating ornament restricted 



to marginal crenulations ; a hypotype from the upper Eagle Ford Shale of 



Texas (locality 15, U.S.G.S. 7539) ; U.S.N.M. 132159. 

 Fig. 15. Interior view (X2) of a large left valve showing internal reflection 



of ornamentation, marks of the attachment area, and the normal position 



of the muscle scar; a hypotype, the original of Stanton's plate 4, figure 5 



(1893) (locality 4, U.S.G.S. 833) ; U.S.N.M. 22859a. 

 Fig. 16. Interior view (X2) of a left valve showing nature of cardinal area, 



denticles, muscle scar, and internal reflection of the ornamentation; a 



hypotype from Colorado (locality 29) ; U.S.N.M. 8354. 

 Fig. 17. Interior view (X2) of a left valve showing fine interior lines on 



inner surface, denticles, cardinal area, and muscle scar ; a hypotype from 



the zone of Prionocyclus Wyoming ensis wyomingensis (Juana Lopez 



equivalent), near Casa Salazar, N. Mex. (locality 17; U.S.G.S. 7993); 



U.S.N.M. 132160. 

 Fig. 18. Interior view (X2) of a left valve; hypotype illustrated by Meek 



on plate 1, figure la (1876), from Vada del Chama, N. Mex. (locality 



31) ; U.S.N.M. 20255. 



Plate 2 

 Lopha lugubris (Conrad) 



Fig. 1. Lateral view (X2) of an unusually elongate right valve showing 

 strong lamellae developed at beginning of plicate stage of valve, and 

 weak plicae; a hypotype from the upper Eagle Ford Shale of Texas 

 (locality 15, U.S.G.S. 7539) ; U.S.N.M. 132161. 



Fig. 2. Lateral view (X2) of a typical plicate right valve, showing abrupt 

 formation of plicae at margin of smooth stage; hypotype illustrated by 

 Stanton (1893, pi. 4, fig. 2), from Huerfano Park, Colo, (locality 3, 

 U.S.G.S. 827) ; U.S.N.M. 22860a. 



Fig. 3. Lateral view of a right valve (X2) ; a hypotype from Rattlesnake 

 Buttes, Colo, (locality 2, U.S.G.S. 747) ; U.S.N.M. 22008a. 



Fig. 4. Lateral view (X2) of an unusually elongate, curved, plicate right 

 valve ; a hypotype from the zone of Prionocyclus wyomingensis wyoming- 

 ensis (Juana Lopez equivalent) near Casa Salazar, N. Mex. (locality 17, 

 U.S.G.S. 7993) ; U.S.N.M. 132162. 



Fig. 5. Lateral view (X2) of a coarsely plicate right valve showing sharp 

 demarcation between smooth stage and plicate portion of valve; a hypo- 

 type from near Mancos, Colo., in the Juana Lopez equivalent (locality 10, 

 U.S.G.S. 2019) ; U.S.N.M. 132163. 



Fig. 6. Lateral view (X2) of a plicate right valve characteristic of the 

 species, showing abrupt origin of plicae, and reflection of attachment sur- 

 face on smooth stage of valve; a hypotype from the upper Eagle Ford 

 Shale of Texas (locality 15, U.S.G.S. 7539) ; U.S.N.M. 132164. 



Fig. 7. Lateral view (X2) of a right valve showing reflection of attachment 

 surface on smooth stage, and restriction of plicae to marginal area. This 

 form is intermediate between plicate and nonplicate types. A hypotype 

 from near Mancos, Colo, (locality 4, U.S.G.S. 833) ; U.S.N.M. 22210b. 



