8 PROCEEDINGS OF THE NATIONAL MUSEUM vol.76 



Locality and geologic Jiorizori. — Plaza, San Antonio, State of San 

 Luis Potosi, with the typical form ol the species; basal part of the 

 Chicontepec formation, probably lower Eocene. 



Cotypes and paratypes. — Cotypes (Cat. No. 371007, U.S.N.M.), 

 one entire specimen and a horizontal and a vertical section, deposited 

 in the United States National Museum. Paratypes, similar to the 

 cotypes, in the Scripps Institution of Oceanography. 



DISCOCYCLINA CRISTENSIS (Vaughan) Vaughan 



Plate 2, figures 1, 2 



1924. Orbitoclypeus ? cristensis Vaughan, Geol. Soc. Amer. Bull., vol. 35, 



p. 814, pi. 36, fig. 8. 

 1928. Discocyclina cristensis Vaughan, in Cushman, Foraminifera, their 



Classification and Economic Use, p. 342. 



The following is an edited copy of the original description of the 

 species : 



Test small, discoid. Megalospheric form, 2 mm. in diameter; thickness not 

 known, but the test is obviously thin and waferlike. Surface of test reticulate, 

 apparently without papillae; if present, very small. 



There is a single spherical embrj^onic chamber, 100/tin diameter. The cham- 

 ber cavity is filled with calcite which is cracked, but no dividing wall could be 

 discerned. The chamber wall is relatively thick, about 12^, or about one-eighth 

 the total diameter of the chamber. 



The equatorial chambers vary considerably in size and proportions. Usually 

 the radial length exceeds the tangential width. Near the center the dimensions 

 are about 37m long by 25iU wide; about 0.6 mm. from the center they are about 

 50/x long by 31m wide; near the periphery some chambers are squarish, 38m long 

 by, ■38m wide. The shape is oblong or squarish. Although the chambers are 

 approximately concentric, there is irregularity, as the illustration shows. The 

 lateral walls of the chambers in successive cycles alternate with each other in 

 position, and thereby produce a slight zigzagging of the boundaries between the 

 chambers in successive cycles, but the zigzagging is so slight that the chambers 

 are usually subrectangular in form. 



Locality. — El Cristo, Vera Cruz, Mexico. El Cristo well No. 1, depth 3,775- 

 3,785 feet. Specimen received from Mr. W. S. Adkins, of the "Aguila" Petro- 

 leum Co. 



Geologic horizon. — Supposed to be Eocene, Chicontepec. 



Tyye.—Csii. No. 371008, U.S.N. M. 



The receipt of additional specimens since the publication of the 

 original description renders possible a more complete description. 

 Two specimens have diameters as follows: (a) 1.25 mm., (6) 2 mm. 

 Thicknesses, (a) 0.17 mm., {h) 0.50 mm. The surface is reticulate 

 with minute papillae, which are from 40/^ to 80/x thick. 



The embryonic apparatus consists of a subspherical initial chamber 

 of about 100/x in diameter, appressed against which is a second 

 chamber lOO^c long and SOju across. The longer diameter is parallel 

 to the contact between the chambers. The second chamber curves 

 on one side of the initial chamber. Between the two ends of the 



