132 AN INTRODUCTION TO THE STUDY OF FOSSILS 



1. Sketch specimen, top view, noting septa, fossula. 



2. How was the calcareous plate secreted ? the septa ? 



3. What is possibly the origin of the fossula ? 



Heliophyllum (Figs. 49, 2). Devonian. 



Coral usually a single cup, not compound ; septa numerous, 



slightly twisted near center of coral and thickened on their sides 



by conspicuous vertical ridges (carinae). 

 (Name from Greek helios, sun, + phyl- 

 lon, leaf (coral) because of the septa 

 radiating conspicuously like the rays of 

 the sun.) 



H. halli from the Hamilton forma- 

 tion of eastern North America is one of 

 the most abundant American species ; 

 in this as in all true Heliophyllums, 

 carinae are lacking for some distance 

 from the apex of the cup, and then 

 appear only gradually. It thus in its 

 individual development passes through 

 a stage in which in this respect it is 

 similar to Streptelasma, a Tetracorolla 

 coral ranging from the Ordovician to 

 the Devonian. 



Fig. 4g. — The coral Helio- 

 phyllum halli E. and H. 

 from the Hamilton (Middle 

 Devonian) formation of 

 New York. This limestone 

 mass was deposited by a 

 single individual, as can be 

 told by the septa (s.) radiat- 

 ing from a center. The 

 flesh of the animal rested 

 upon this mass and within 

 the central, cuplike cavity ; 

 it covered only the upper 

 portion. Natural size. 

 (From Hall.) 



I . Sketch {a) view of entire specimen, 

 showing both side and top, (b) horizon- 

 tal section near top, (c) horizontal sec- 

 tion near tip. Note septa, carinae, 

 dissepiments. 



2. How were the septa formed? the carinae ? the dissepi- 

 ments ? 



3. What does the section i c suggest as to the ancestry of 

 Heliophyllum ? 



Columnaria (Fig. 50). Ordovician to Devonian. 



This is a closely compound coral with prism-shaped corallites 



(whence the name from Latin columnarius, formed of columns). 



