72 



EOCENE AND LOWER OLIGOCENE CORAL FAUNAS. 



the middle of the lateral faces; correspond to all cycles of septa. Tnter- 

 costal furrows not ver)' deep. Septa from 18 to 24 in number, very slightly 

 exsert. Their surfaces are beset with small, rather blunt, spines. The 

 columella is traljecular, and in the lower portion of the corallum is very 

 poorly developed; in the upper portion it is reinforced by lobes sent up 

 from the inner ends of the septa. Upper surface papillate. Calice very 

 shallow. 



Greater diameter of calice . 

 Lesser diameter of calice.. 

 Height of corallum 



Mm. 

 1.7 

 1 

 4.3 



Mm. 

 2 



1.25 

 3.2 



Mm. 

 2 



1.75 

 6 



Localities. — Dry Crcck, Jackson, Mississippi ; Montg-omery, Louisiana. 



Geologic occurrence. JacksOlliail StagC. 



Types. — From collection of T. H. Aldrich in the United States National 

 Museum; and Wagner Free Institute of Science. 



Specimens. — Uiiltcd Statcs Natloiial Museum and Wagner Free Institute 

 of Science, Philadelphia. 



In the character of its columella tliis little species resembles the species 

 of Platytrochus. 



The following observations were made on a specimen with 18 costaj and 

 18 septa: It is slightly curved in the plane of the longer transverse axis of 

 the calice, and one side of the corallum is a little more convex than llie other. 

 Of the 18 costJE 12 persist to the top of the pedicel, and there are faint indi- 

 cations of 6 on the pedicel. The septal arrangement is in six systems, each 

 system containing two complete cycles, and there are six se})ta of the third 

 cycle. The sei)ta of the third cycle arise, one on each side of three septa 

 of the first cycle. These three septa of the first cycle are the two at the 

 ends of the longer, transverse axis of the calice and one on the more convex 

 side of the corallum. Tliis method of intercalation (^f the septa of the third 

 cycle would make the corallum bilaterally unsymmetrical, i. e., seven septa 

 would lie on one side of a plane through the vertical axis of the corallum paral- 

 lel to the longer transverse axis of the calice, and nine would lie on the other 

 side. In order to maintain the bilateral symmetry, a twisting takes place, 

 by which one of the tertiary septa stands at one end of the longer transverse 



