l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



depends mainly on the state of preservation of the test. The diameter 

 varies from 2 to 5 mm, the thickness from i to 2.4 mm. The central 

 inflated part has a diameter ranging from 2 to 3 mm, the rim, when 

 present, a width of 0.3 to i.o mm. Surface ornamentation consists 

 of 6 to 8 heavy costae radiating from the center of the test to the 

 inner edge of the rim. These costae are separated from each other by 

 deep grooves about 0.15 mm in width and of about the same depth. 

 The individual costae increase rapidly in width as they approach the 

 rim, and some show a tendency to bifurcate. The apex of the test is 

 variously ornamented. Some specimens have a strong central boss, as 

 much as 0.38 mm in diameter, directly over the center and separated 

 from the radiating costae by a deep groove. In others, there are two 

 much smaller bosses, whereas some specimens have only a depression 

 formed by the intersection of the grooves, separating the individual 

 costae. The entire surface of the test shows rather strong reticula- 

 tion. The rim, when preserved, is rather sharply demarked from the 

 remainder of the test ; flat to slightly undulating, and without orna- 

 mentation except the reticulation. 



In horizontal sections the equatorial chambers near the center are 

 lozenge-shaped, but near the periphery they become regularly hex- 

 agonal. They increase in size as they approach the periphery. Those 

 near the center of the test have a radial diameter of about 30 fi and a 

 transverse diameter of about 50 jj. ; those near the periphery have a 

 radial diameter of 80 /x and a transverse diameter of about 75 jn. The 

 height of the equatorial layer at the center is 50 ju. It increases 

 rather rapidly in height until at the periphery its height is 275 fi, 

 measurements including both walls. 



In vertical section, the lateral chambers are much restricted and 

 shortened by the very heavy pillars over the center. These pillars vary 

 from 0.3 to 0.55 mm in diameter. There are about 10 lateral chambers 

 on each side of the equatorial layer over the center. The number 

 decreases toward the periphery. On the rim there are no lateral 

 chambers over the equatorial layer. The lateral chambers over the 

 center at the periphery have a length of about 90 fx, a height of about 



The foregoing description is based on sections of microspheric 

 individuals, as the megalospheric form has not been observed. 



Localities and geologic horizon. — Mercer's Creek, Antigua, col- 

 lected by W. R. Forrest, Antigua formation, and Arbol Grande near 

 Tampico, Tamaulipas, and Rio Pantepec, just above El Contento, 

 Canton of Metlaltoyuca, State of Puebla, Mexico, in the Meson for- 

 mation. The species occurs in the middle Oligocene, and it may range 

 into the upper Oligocene. 



