NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 63 



would occupy such a well-defined ecologic niche than that two closely 

 related species or subspecies would be living together and competing 

 for the same niche. 



Recognition of the variety is of additional importance since it may 

 be the source from which contemporary and younger species of 

 Lopha, having generally similar features, originated. Such ostreids, 

 mostly undescribed, occur at various localities and stratigraphic 

 levels in the Western Interior and will be the object of future study. 

 They are not found in older sediments. 



The morphologic distinctions between L. bellaplicata hellaplicata 

 and variety A have been previously discussed under "Remarks" for 

 the former subspecies. 



Stratigraphic and geographic occurrence. — ^The variety occurs 

 throughout the Middle Turonian "Pugnellus Sandstone" (Codell 

 Sandstone member) of the Carlile Shale at localities 41, 58, 59, 60, and 

 61 in Huerfano Park, Colo. Rare marginal variants of the Texas and 

 Colorado collections of L. hellaplicata hellaplicata approach this 

 form, but none attain it. 



Illustrated specimens.— Leit valves: U.S.N.M. 22011a, d; 132249; 

 U.M.M.P. 38051, 38052; associated right valves, illustrated; 

 U.S.N.M. 132259, U.M.M.P. 43413; hypotypes. Measured speci- 

 mens, not illustrated : U.S.N.M. 132301-132303 ; U.M.M.P. 43406. 



LOPHA BELLAPLICATA NOVAMEXICANA new subspecies 



Plate 7, figures 1-19; plate 8, figures 1-9 



DESCRIPTION 



Material. — About 100 well-preserved specimens (measured), pre- 

 dominantly left valves, from 4 localities in New Mexico and 8 localities 

 in Colorado, including ontogenetic series and 2 large suites of speci- 

 mens from single localities. 



General form. — Summary of measurements presented in table 5. 

 Shell attaining moderate size ; inequivalve, left (lower, attached) valve 

 slightly larger, much more convex than right valve ; slightly to moder- 

 ately inequilateral, prosocline. Valves close-fitting, outline moder- 

 ately variable ; typically subovate, commonly subquadrate or elongate- 

 ovate parallel to axis of inclination, rarely rounded (pi. 7, figs. 1-5, 

 10-12, 14-19; pi. 8, figs. 7-9 typical of subspecies). Height greater 

 than length in most specimens. Anterior margin slightly curved dor- 

 sally and ventrally, moderately rounded medially. Ventral margin 

 moderately and evenly rounded ; ventroposterior corner more narrowly 



