74 EOCENE AND LOWER OLIGOGENE CORAL FAUNAS. 



The columella in this genus is derived in the same way as in the new genus 

 Aldrichia described in this monograph. (See PI. IV, fig. 24.) 



In the definition of the genus Platytrochus the following modification 

 must be made : 



Columella false, formed ):>)' the fusion of lobes from the inner margins 

 of the septa, or by the fusion across the axial space of the inner margins of 

 the septa. 



This necessitates the removal of Platytrochus from the alliance Placo- 

 trochoida to which Duncan referred it. 



The mode of costal increase is very important. This is noted on page 

 7G, in the description of P. goldfussi. 



The following notes on the structure of the septa and wall may be 

 added: 



The septal margin is divided by a notch at the wall into a portion inter- 

 nal to the wall and one external thereto. The septa are solid, and are 

 composed of ascending trabecular, whose courses are marked by rows of 

 granulations. There is a line of trabecular divergence approximately half- 

 way between the wall and columella. Each trabeciila, where it emerges at 

 the septal margin, has coi'responding to it a prominent tooth. The teeth are 

 not especially sharply pointed. 



The columella has already been described in detail. 



Wall. — In the distal portion of a septum there ai-e several sets of calcifi- 

 cation centers alongside one another, and between the enlarged ends of the 

 septa a line of fusion can be distinguished (see PI. V, fig. 8). The theca is 

 false. In the thin inner portion of the septa there is a single series of calci- 

 fication centers, and in the thicker distal portion there are several series of 

 centers. 



Platytrochus stokesi (Lea). 



PI. IV, tigs. 20 to 24; PI. V, figs. 1, la, and 8. 



1833. Turbinolia utokesii Lea. Contrib. to GeoL, p. 194, pi. vi, fig. 207. 



1838. Turbinolia st(>l;esii Michelotti. Spec, zoopbyt dil., p. 50. 



1S45. Endopachys (pars) Lonsdale. Qnart. Jour. Geol. Soc. Loudon, Vol. I, p. 514, 



figs, b and c. 

 1848, Turhinnlia ntulwuii Broun. Index Pal., p. 131G. 

 1848. Platytrochus stokesii Milne-Edwards and Haiine. Annales sci. uat., 3d ser., 



Vol. IX, p. 247, pi. vii, fig. 7, 



