NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP KAUFFMAN 7 



The Austin has been considered totally Coniacian in the past, although 

 locally, the lowermost Austin chalks contain a Late Turonian fauna. 

 The calcarenite unit is, without doubt, Late Turonian in age and 

 faunally allied with pre- Austin sediments. 



HISTORY 



Attempts to treat the Lopha luguhris group in the past have 

 encountered the many pitfalls inherent in taxonomic study of the 

 Ostreidae. It has been treated as a single variable species (Stanton, 

 1893 [1894], pp. 58, 59) and as a series of related species, some of 

 which appear valid, others merely environmental variants of described 

 forms. The problems which have produced such inconsistency are 

 those that have generally affected the taxonomy of ostreids in the 

 past: Inability to distinguish environmental control on shell form 

 from genetic shift ; failure to define adequately the limits of specific 

 variability through the study of small and geographically restricted 

 samples rather than analysis of numerous, widely distributed "popula- 

 tions" ; application of typologic paleontology ; limited knowledge of 

 modern representatives of the family ; insufficient stratigraphic data ; 

 and others. It is not surprising that the group has a complex nomen- 

 clatural history in previously published studies. 



Conrad's original description (1857, p. 156, pi. 10, figs. 5a, b) 

 was based on a few small, densely plicate specimens with large 

 attachment areas. These were obtained from calcarenites typical of 

 the lower Juana Lopez member (upper Carlile Shale: zone of 

 Prionocyclus macombi Meek and P. Wyoming ensis Wyoming ensis) 

 in New Mexico and all belong to Lopha luguhris s. 1. Shumard 

 (1860, p. 608) later recognized a larger, more coarsely plicate, and 

 somewhat older form, Ostrea hellaplicata, in the upper Eagle Ford 

 Shale of Texas. White's Ostrea blacki (1880, p. 293, pi. 4, figs. 1, 2) 

 appears to be erected on worn, smoother, ecologic variants of L. 

 hellaplicata hellaplicata. The two forms occur in approximately time- 

 equivalent strata. 



These names were used by a number of authors without much 

 change until Stanton (1893 [1894], pp. 58, 59) placed all members 

 of the group into synonymy with L. luguhris Conrad, regarding them 

 as ecologic variants of a single species. Stanton's concept has been 

 generally perpetuated in this country, although the other names are 

 used occasionally in fieldwork, on collection labels, and in unpublished 

 faunal lists. In Mexico, however, Bose (1913, pp. 47, 48) recognized 

 L. luguhris, L. hellaplicata, and L. hlacki as distinct species, but 



