4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



The zone of Lopha lugubris lies predominantly above that of L. 

 hellaplicata hellaplicata, but their ranges overlap slightly (fig. 1), 

 At two known localities in Texas, the species are found together in 



Fig. 1. — Stratigraphic range of oysters in the Lopha lugubris group from 

 Colorado, New Mexico, and Texas, and proposed correlations. Colorado 

 stratigraphy taken along the east flank of the Front Range (Canon City, Pueblo, 

 Huerfano Park areas). New Mexico section interpolated from Cerrillos and 

 Carthage sections of Rankin (1944) and from stratigraphic data on collections 

 made between Cerrillos, N. Mex., and Trinidad, Colo. Texas section generalized 

 for central and northeast Texas. 



the upper 2 or 3 feet of the Eagle Ford Shale. They are distinct in 

 this zone of overlap, and do not intergrade. L. lugubris does not 

 range below this level, as does L. hellaplicata hellaplicata. It 

 ranges upward, however, above the range of L. hellaplicata hellapli- 

 cata, through the calcarenite bed between typical Eagle Ford Shale 



