DESCRIPTIONS OF SPECIES. 151 



are not approximate have a raised acute edge, and the coralHtes whose 

 walls are free are ornamented externally by crowded, minute, granulated, 

 acute costse. Septa not exsert, margins regularly and sharply dentate, the 

 trabeculse directed horizontally, or almost horizontally, inward. Some 

 septa are represented by horizontal spines placed one above another. 

 None of the septa examined showed any pei-fo rations. Septal an-angement : 

 six systems, two cycles, the first of which reaches the columella; frequently 

 members of the third cycle are present, then two or even three septa of the 

 second cycle may be fused to the columella. In this case the appearance 

 is eight systems of two cycles, or the arrangement apparently is irregular. 

 Endothecal dissepiments are present. They are thick, not numerous. A 

 little exotheca sometimes present. Columella tall, styliform, rather slender. 



Locality . — Jackson, Mississippi. 



Geologic occurrence. — Jacksouian stage. 



Type. — United States National Museum. 



Genus STEPHANOCCENIA Milne-Edwards and Haime. 

 Stephanoccenia fairbanksi sp. nov. 

 PI. XVII, figs. 10 to 11a. 

 (Figs. 10 and 10a, Stephanoccenia fairbanksi var. columnaris var. nov.) 

 Form of corallum explanate or columnar. The specimens possessing 

 the explanate method of growth may be considered the typical form ; those 

 with the columnar method of growth, St. fairbanksi var. columnaris var. nov. 

 The sizes and general appearance of the two forms are shown in PI. XVII, 

 figs. 10 and 11. The corallites are polygonal in form, usually hexagonal, 

 are joined directly by their walls or by very short costse. The greater diam- 

 eter of the corallites is very constantly 3.5 nun. Some corallites may be 

 smaller and some slightly larger, but 3.5 mm. is the usual diameter. 

 The walls between two corallites on an unweathered surface or in a 

 section are stout and usually solid; they are almost a millimeter thick. 

 They are clearly pseudothecal. In places the corallites may be joined by 

 very short costte; then open vertical spaces may exist between the costse. 

 None of the specimens show the upper edge of the wall in its original condi- 

 tion ; therefore its ornamentation can not be described. The septa are in three 

 complete cycles; the members of the first and second cycle fuse to the 

 columella; those of the tliird cycle fuse to the sides of those of the second (?). 

 (There is no way of dlfi'erentiating the first from the second cycle.) They 



