12 PROCEEDINGS OP THE NATIONAL MUSEUM vol.76 



relatively thick, as much as 60ju, and are pierced by numerous, mi- 

 nute, cribriform perforations, which are about 2/x in diameter, some 

 slightly smaller, others slightly larger. 



Lateral chambers well developed and distinctly demarked. The 

 number of layers in the thick umbonate area is as many as 20 on 

 each side of the equatorial layer. Outside the umbonate area the 

 number decreases to eight or less, and at the actual periphery 

 there are about two. The equatorial layer does not appreciably pro- 

 trude at the peripherj^. The ends of the chambers are formed by 

 definite pillars, of which at least many have their inner ends at the 

 equatorial layers. Most of the pillars do not show definite increase 

 in thickness toward the periphery, but some do. The thickness is 

 not uniform, but ranges from 16^1 to about 60^1, with SO/z as an appar- 

 ent maximum. The length of the chamber cavities ranges from 

 about 40m to 160^t, and the height ranges from 8^ to 32^; 24iu is com- 

 mon. The roofs range from 8/jl to 16ju thick and are pierced by 

 cribriform perforations similar to those of the roofs and floors of the 

 equatorial chambers. Longitudinal perforations, tubular cavities, 

 appear also to be present in the pillars. The chambers form rather 

 definite tiers, the pillars being at the sides of the tiers. In places 

 the ends of the chamber roofs on opposite sides of the pillars alter- 

 nate with each other in position. The pillars emerge on the surface 

 to form the granulations already described. 



Localities and geologic occurrence. — This is the commonest species 

 of Discocyclina in the Mecapala Hills southwest of Tantoyuca, State 

 of Vera Cruz, Mexico, and it is abundant at many places in that 

 general area. Its association with Ostrea sellaeformis Conrad and 

 its stratigraphic relations are the basis of the opinion that the 

 horizon is that of the Lisbon formation of the Claiborne group in 

 Alabama — that is, middle Eocene — but it may also occur in beds of 

 upper Eocene age. The field evidence is not decisive. 



Coiypes.—Csit. No. 371009, U.S.N.M. The actual description of the 

 species is based on a single excellent specimen (pi. 3, fig. 1) from locality 

 M.108 v., Zardo Creek, 0.7 km. southwest of Tierra Colorada, Canton 

 Tantoyuca (collected by T. W. Vaughan), and specimens in the 

 matrix and three thin sections of rock from Buena Vista Creek, 

 Mecapala Hills, Las Piedras coordinates, 1,050 m. north and 2,610 m. 

 east (collected by G. E. Ebmeyer and H. L. Rau). Two thin sec- 

 tions are illustrated by Plate 3, figures 3,4. The cotypes are depos- 

 ited in the United States National Museum. Plate 3, figure 2, 

 illustrates a split specimen, a paratype, from locality M. 104 V., 8 

 km. northwest of Tantoyuca on the road to Dos Caminos (collected 

 by T. W. Vaughan). 



Discocyclina cusJimani is a flat, distinctly umbonate, densely gran- 

 ulate species, which has well-developed pillars and well-defined 



