314 PROCEEDINGS OF THE NATIONAL MUSEUM vol.86 



Other speciTnens.—V.^.'^M. no. 497843. 



Occurrence. — This species has been recorded only from the Meson 

 formation, middle to upper Oligocene. 



OPERCULINOIDES SEMMESI Vaughan and Cole 



Plate 19, FiGintES 1-6 



1936. Operculinoides semmesi Vaughan and Cole. Proc. U. S. Nat. Mils., vol. 

 83, p. 491, pi. 37, figs. 10-13 and probably 14 ; pi. 38, figs. 1-4 and prob- 

 ably 5 and 6. 



In early work I included O. antigiiensk and O. semmesi in a sin- 

 gle species, with a considerable range in variation, but Vaughan 

 and Cole have separated slightly smaller specimens, with a thinner 

 test and fewer chambers in the final whorl, as O. semmesi. This 

 species is similar to O. antiguemis in general appearance, but, in 

 large numbers of specimens seen by me, is generally smaller and 

 thinner, though the range in diameter (1.75 to 2.8 mm) is almost 

 the same for the two species. Thickness, 0.55 to 0.65 mm. 



Sections show 3 to 31/0 whorls, with 18 or 19 chambers in the final 

 whorl. The septa show the same characteristic curvature as O. anti- 

 giie')isis. It is still thought that 0. semmesi may be only a variety 

 or a dwarf race of 0. anfigu^ensis, since botli liave the same range in 

 Mexico and have not yet been found to occur in the same localities, 

 suggesting that the dijfferences may be due to local changes in en- 

 vironment. 



Plesiotypes.—U. S.^.M. nos. 497844 and 497845. 



Other specimens.— U.S. ^^.M. nos. 497846 and 497847. 



Occurrence. — Believed to be restricted to the Meson formation. 



OPERCULINOIDES PALMAREALENSIS, new species 



Plate 13, Figure 8 ; Plate 18, Figure 1 ; Plate 22, Figures 7, 8 



Test small, stoutly lenticular, completely involute, with an acute 

 periphery. The septa show as gently curved lines of clear shell ma- 

 terial radiating from a large, clear central mass. Diameter, 1.8 to 

 2.2 mm ; thickness, average 0.9 mm. 



Sections show the septa to be sharply recurved, somewhat as in 

 Operculinoides antiguensis and O. semmesi., but the curvature is not 

 so abrupt, the coiling is less regular, and the test is consistently 

 smaller and thicker in proportion to the diameter. Mature speci- 

 mens usually show 4 whorls, with 18 to 20 chambers in the final 

 whorl. The chambers are somewhat irregular in size and shape. 



Cotypes.—V.SI^M. nos. 49784^-497850. 



Occurrence.— AXaz^w formation (Huasteca formation of Muir), 

 lower Oligocene. The description is based on cotypes from Meca- 

 tepec Well no. 5, Mecatepec, Veracruz. 



