NO. 10 AMERICAN SPECIES OF LEPIDOCYCLINA VAUGHAN 3I 



diameters of the inner chamber are respectively 0.97 and 0.61 mm. 

 The thickness of the chamber wall is 0.08 mm. 



The radial diameter of the equatorial chambers ranges from 75 to 

 100 fx and the transverse diameter from 75 to 130 fi. The transverse 

 usually exceeds the radial diameter in length. The height of the 

 equatorial chamber at the center in a microspheric individual is about 

 150 fi, at the periphery about 320 yx. In plan, they range from short- 

 spatulate to arcuate. 



The lateral chambers have thick roofs and floors, and are long, 

 depressed. Although many chambers are disposed in regular tiers, 

 some irregularly overlap the layers above and below. The roofs are 

 often slightly arcuate. The maximum on each side of the equatorial 

 layer at the center is 12. The number decreases regularly as the 

 periphery is approached, until for a distance of about 0.4 mm from the 

 edge the equatorial layer is not covered. The length of the chambers 

 in the center of the test ranges from no to as much as 190 ju.. The 

 height of the chamber cavities and the thickness of the roofs and 

 floors are about equal, each ranging from about 20 to 30 fx. 



Pillars are weakly and irregularly developed. Their diameter ranges 

 from 75 to 100 fx. 



Localities and geologic horizon. — About 4.5 km from Chila Cortaza 

 on the road to Tantoyuca, about 10 km east of Tantoyuca (M92V), 

 and 0.6 km southwest of Dos Caminos on the road from Dos Caminos 

 to Tierra Colorada, Canton of Tantoyuca (]\Iio6V), State of Vera 

 Cruz, Mexico, collected by T, W. Vaughan and D. R. Semmes. 

 Upper Eocene, Tantoyuca formation. 



Lepidocyclina semmesi and L. tantoyucensis both belong to the 

 subgenus Nephrolepidina and are so closely related to L. {Nephro- 

 lepidinu) fragilis Cushman that the senior author has vacillated 

 between referring them to that species and assigning new names to 

 them. By comparing the respective descriptions and illustrations here 

 given, the reasons for specific separation will be obvious. The equa- 

 torial chambers of L. fragilis are in general hexagonal or spatulate ; 

 they are not radially shortened as in L. semmesi and L. tantoyucensis. 

 The differences from each other of the last two species are brought 

 out by the figures on plate 15. 



All three of these species occur in virtually summit beds of the 

 Eocene, L. fragilis in the topmost bed of the Ocala limestone, the 

 other two species in the upper Eocene Tantoyuca formation. Lepi- 

 docyclina chaperi Lemoine and R. Douville from the upper Eocene 

 at San Juan de Pequani, upper Chagres River, Panama, belongs in 

 the same group of species and occupies a very similar, if not identical, 

 stratigraphic position. 

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