488 PROCEEDINGS OF THE iN^ATIONAL, MUSEUM vol. 83 



Operculinoides antiguensis: Oligocene, Antigua formation, island of Antigua, 

 and probably also Meson formation, Tampico Embayment, Mexico. 



Operculinoides forresti: Oligocene, Antigua formation, island of Antigua. 



Operculinoides tuxpanicus: Miocene, Tnxpan formation, Tampico Embayment, 

 Mexico. 



All types are deposited in the United States National Museum. 



The species of Operculina and Operculinoides here described do 

 not exhaust all the species that should be described. There is at 

 least one other in the Meson formation of the Tampico Embayment, 

 but material for adequately characterizing it is not now available. 



The limits of the variation of the species designated as Operculi- 

 noides semmcsi and 0. aniiffucnsis are not yet definitely fixed. The 

 notes made under the caption "Remarks" indicate perplexities that 

 require further consideration. 



Our thanks are due R. Wright Barker for telling us the strati- 

 .graphic horizon of O perculina tuberculata; to XJrsel S. Armstrong 

 ior making some of the preparations ; and to W. O. Hazard, of the 

 United States Geological Survey, and E. C. LaFond, of the Scripps 

 Institution of Oceanography, for making the photographs for the 

 plates. 



Genus OPERCULINA d'Orbigny 



Operculina d'Orbigny, Ann. Sci. Nat., vol. 7, p. 281, 1826. 



OPERCULINA TUBERCULATA, new species 



Plate 35, Figures 1-4 



Test small, with a peripheral keel, compressed, coils expanding 

 slowly. Diameter from outer edge of aperture through center, 1.9 

 mm; diameter at right angles to line through aperture, 1.7 mm; 

 thickness through center, about 0.4 mm. 



The number of chambers in the final whorl of a specimen 1.6 

 mm in diameter is 16 ; the total number of coils in the same specimen 

 is 3. The chamber walls are very slightly curved for their first 

 half but are strongly and evenly recurved as they approach the 

 periphery. The chamber walls are marked externally by costae and 

 rather coarse granules, as shown in the figures. At the center there 

 is a knob that is larger than the costal granulations, about 0.15 mm 

 in diameter. 



("(9^?//;e5.— U.S.N.M, no. 495188. 



Locality. — Cortez Aguada well no, 2, depths 2,000-3,450 feet, 

 5.3 km northeast of Chalahuite and 7.2 km south of Aguada in 

 property Aguada-San Diego Valdemar, Canton of Ozuluama, State 

 of Veracruz, Mexico. Cotypes from depths of 2,625 to 2,800 feet. 

 Specimens received from Dr. W, S. Adkins, of the Aguila Co. 



Geologic horizon. — Upper Eocene, Tantoyuca formation. 



