LONSDALE ON MIOCENE CORALS FROM N. AMERICA. 



49? 



2. Columnaria(?) SEXRADIATA. 



Polymorphous ; tubes polygonal, divergent ; adjacent walls separable, exler 

 nally traversed by indistinct ribs and transverse inequalities ; lamellae variable in 

 width, and simple or grouped, according to age; interstitial laminae not numer- 

 ous; terminal immature star, sides of lamellae vertical, interspaces wide, open; 

 terminal mature star shallow, sides of lamellae thickened obliquely, the thicken- 

 ing extending across and closing the interspaces ; boundary between stars a 

 slight groove; centre of column and star a union of lamellae; additional columns 

 interpolated. 



a. Section of Columnaria sexradiata of the natural size, exhibiting the ten- 

 dency of the columns to separate ; and in the centre, irregularities in the 

 structure of the columns, owing to interference during development. 



b. A terminal star enlarged, to show the characters believed to be connected 

 with the final termination of growth. 



This fine fossil agrees with the Columnaria of Goldfuss in the 

 simplicity of the internal structure, and in the mode of producing 

 additional columns ; but changes in the terminal stars, analogous 

 to those exhibited in the coral under consideration, do not appear 

 to have been noticed in Col. sulcata or the other species described 

 by Professor Goldfuss (Petref. p. 72.). The generic determination 

 is therefore considered doubtful. Corals possibly allied to this 

 fossil have been figured from Maestricht by M. Goldfuss under the 

 name of Astrea angulosa (Petref. pi. 23. f. 7.), and from the 

 muschelkalk of France by M. Michelin by the name of Ast. 

 polyyonalis (Iconog. Zoophytol. pi. 8. f. 1.); but the American 

 polypidom is most clearly not an Astrea, as limited by Ehrenberg, 

 nor does it belong to any of that authority's allied genera, the 

 mode of reproduction being most decidedly not by a subdivisional 

 process. 



The specimens which were examined varied considerably in 

 form, being cylindrical, or lobed, or developed in broad expansions ; 

 yet the plan of growth was the same in every case, the columns 

 radiating abruptly from a central line or imaginary axis, and beino- 



ll3 



