NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP KAUFFMAN Jl 



zone of CoUignoniceras hyatti (Stanton) (late Middle Ttironian), 

 well below the occurrence of L. lugubris. Its position relative to 

 L. bellaplicata hellaplicata in New Mexico is uncertain, however, since 

 the latter is rare in this area, and the two have not yet been found 

 associated. 



The stratigraphic relationship between L. hellaplicata hellaplicata 

 and the subspecies novamexicana can be established in Huerfano 

 Park, Colo. Here, typical examples of L. hellaplicata hellaplicata 

 are found throughout the Codell Sandstone Member ("Pugnellus 

 Sandstone") (pi. 6, figs. 7-9, 12). Below this unit, in the upper part 

 of the Blue Hill Shale Member, septarian limestone concretions con- 

 tain scattered but characteristic examples of the subspecies nova- 

 mexicana (pi. 7, fig. 11). The two forms do not have overlapping 

 ranges in this area, although rare individuals transitional between 

 them occur as marginal variants of each form. This occurrence sug- 

 gests, therefore, that L. hellaplicata novamexicana is characteristic of 

 the lower part of the CoUignoniceras hyatti zone (Blue Hill Shale 

 Member equivalents) and L. hellaplicata hellaplicata marks the upper 

 part of the C. hyatti zone (Codell Sandstone Member: "Pugnellus 

 Sandstone" of older authors). If future collections prove this to be 

 true over a broad area in the Western Interior, these ostreids will have 

 particular importance as stratigraphic markers, since the faunas of 

 these two units overlap in almost every other respect. The subspecies 

 novamexicana occurs at localities 62 through 73, described in detail at 

 the end of this report. 



Illustrated and measured specimens. — Holotype, a typical left valve 

 with the interior excavated, U.S.N.M. 132267 (pi. 7, fig. 10). 

 Figured paratypes, left and right valves, U.S.N.M. 22012 ; U.S.N.M. 

 132260-132266 inclusive; U.S.N.M. 132268-132282 inclusive; 

 U.S.N.M. 132286-132288 inclusive. Measured, unfigured paratypes, 

 U.S.N.M. 132252-132257 inclusive, 132290. University of Michigan 

 Museum of Paleontology (U.M.M.P.) 43480, 43481. Sectioned 

 specimen, discussed, U.S.N.M. 132289. 



COLLECTING LOCALITIES 



Collecting localities and stratigraphic information are cited as they 

 appear in the Mesozoic catalogs of the U. S. Geological Survey and 

 U. S. National Museum. In many cases, data available for older 

 collections are brief and generalized. Many such collections have 

 been omitted from this study for this reason. Others have been 

 incorporated because it is obvious from the locality data and from 



