306 PROCEEDINGS OF THE NATIONAL MUSEUM vol.86 



do most of the other groups, and moreover they have frequently 

 suffered in the past from very inadequate descriptions and figures. 



STRATIGRAPHY 



John M. Muir (1936) has recently published an excellent account 

 of the stratigraphy of the area in which the present collections 

 were made, and he clearly differentiates the various horizons. I havQ 

 been accustomed, in common with many workers in Mexico, to a 

 slightly different nomenclature, such as Alazan in place of Huasteca 

 formation, Cole's Guayabal in place of ver Wiebe's Tempoal, and 

 Velasco rather than Tamesi. Though there is little doubt as to the 

 soundness of Muir's reasons for changing the nomenclature, both 

 systems are given in the present account since the ages of the beds 

 containing the species described were determined by means of the 

 smaller Foraminifera as described by Nuttall (1932) in his account 

 of the Upper and Lower Alazan and by W. Storrs Cole (1927, 1928) 

 in his papers on the Chapapote and Guayabal. As there is some 

 doubt as to the exact equivalence of the Huasteca to the Alazan as 

 understood by Nuttall and also a possibility that the Guayabal of 

 Cole represents a higher horizon than ver Wiebe's Tempoal (as 

 exposed at the type localities of these formations), it has been 

 thought better to give the older nomenclature and, in parentheses, 

 what is considered to be the equivalent horizon of Muir. 



The nomenclature alternative to that of Muir may be found in 

 a recent publication of the writer (Barker, 1936). 



PREVIOUS PUBLISHED WORK 



Beginning with Cushman's monograph, "American Species of 

 Opei'culina and Heterostegina''' in 1921, a large number of species 

 referred to Operculina and NummuUtes have been described from, 

 the New World, though it had long been denied that true Num- 

 muUtes existed there. The greater number of species have been 

 contributed by Cushman, the elder and younger Kutten, Willard 

 Berry, Mrs. Palmer, W. Storrs Cole, Dr. Vaughan, and Gravell and 

 Hanna. The species of both L. and IM. G. Kutten are in general 

 well described, with fairly adequate illustrations; those of Cushman 

 are very incompletely described, and in many cases sections either 

 are not illustrated or are so badly illustrated as to be of little value ; 

 the work of Willard Berry is similar to his work on the Peruvian 

 species of Lepidocycliria and may be neglected in the present resume. 

 Of most importance is a re<;ent account by Dr. T. Wayland Vaughan 

 and W. Storrs Cole (1036) entitled "New Tertiary Foraminifera 

 of the Genera Operculina and Operculinoides from North America 



