80 EOCENE AND LOWER OLIGOCENE CORAL FAUNAS. 



and over the wall. A continuation of this mode of development ultimately 

 results in the normal adult form, as shown in PI. V, figs. 17, etc. 



There is considerable variation in the curving of the septal margins 

 around the periphery of the corallum. In some specimens the peripheral 

 part of the corallum is quite thin, the costal margin being rounded so abi'uptly 

 into the septal margin that they almost make an angle with one another. 

 In other specimens the periphery of the corallum is quite thick, the costal 

 margin then passing by a gentle curve into that of the septum. This is the 

 only especially noteworthy variation that I have noticed. 



Additional localities. — Uppcr layer, Sowilpa Creek and Coifeeville Landing, 

 Tombigbee River, Alabama; Wautubbee Hills, Mississippi; 2 miles south- 

 east of Hickory, Newton County, Mississippi; 3 miles northeast of Newton, 

 Newton County, Mississippi; 1 mile south of Hickory, Mississippi; 6 miles 

 west of Desoto Station, Clarke County, Mississippi; 1 mile south of Hickory, 

 Mississippi; 8 miles south of Hickory, Mississippi; railroad 4 J miles east 

 of Newton, Mississippi; near Mount Lebanon, Louisiana; Pittman's mill, 

 Claiborne Parish, Louisiana; Shipps Ford, Bastrop County, Texas; Ala- 

 bama Bluff", Trinity River, Houston County, Texas. 



Geologic eccurrence. LoWCr Clalbome. 



The only other species of this genus known to me are Discofrochus 

 micheUottii M.-Edw. and H., from the Miocene of Turin, Discotroclius duncani 

 Reuss, Miocene of Austro-Hungary, and Biscotrochus f alternans Sokolow, 

 Lower Oligocene of Jekaterinoslaw, southern Russia. 



Genus SPHENOTROCHUS Milne Edwards and Haime. 



Sphenotrochus nanus (Lea). 

 PI. V, figs. 20 to 24, fig. 22 ( !). 



1833. Turbinolia nana Lea. Contrib. to Geol., p. 195, pi. vi, fig. 209. 



1838. Turhinolia nana Miehelotti. Spec, zoophyt. dil., p. 55. 



1848. tSphenotrochus "' nanus Milue-Edwards and Haime, Anuales sci. nat,, 3d ser.. 



Vol. IX, p. 24G. 

 18C1. Sphenotrofihus f nanus de Fromentel. Introd. il I'Etude de tolyp. foss., p. 93. 

 1890. Platiifrochus nanus Lea sp. dub. de Gregorio. Mou. de la Faune eoceuique de 



I'Ala., p. 255. 



Description of Lea's type, in the Academy of Natural Sciences of Philadelphia. Fomi CUUeatC 



transverse outline elliptical. Strong costse of nearly equal prominence cor- 

 responding to all of the septa; those on the lateral faces corresponding to 



