1 82 W. I. Robinson, 



that an early ontogenetic stage with only eight mesenteries, 

 commonly referred to as the Edivardsia stage, has been found 

 in many lines of the Anthozoa. 



First Coral Fauna. 



Undoubted forms of the class Anthozoa representing the sub- 

 classes Alcyonaria, Tabulata, and Tetracoralla of the Zittel-East- 

 man classification have been found in the lower part of the 

 Middle Ordovician. The first of these groups to appear are 

 the Alcyonaria (Octocoralla) represented by Stylarcea parva 

 (= Tumularia parva Robinson 1916) and Fletcheria incerta. 

 Tumularia parva is found near the base of the Middle Ordo- 

 vician (Chazy) of the Lake Champlain-Montreal area and the 

 Mingan Islands, and in the higher Stones River series of Vir- 

 ginia and Tennessee. Fletcheria incerta is also found in the 

 Chazy of the above mentioned Canadian localities. Tetradium 

 syrin go p oroides and Columnaria alveolata are other compound 

 corals found in the Stones River series and represent respec- 

 tively the Tabulata and the Tetracoralla. Columnaria alveolata 

 continues into the later Ordovician formations, where it is 

 associated with a number of other individual and colonial 

 Tetracoralla. 



From the above facts it is apparent that at the time of their 

 first appearance as fossils in the Middle Ordovician the Anthozoa 

 were already differentiated into three great groups, the sub- 

 classes Alcyonaria, Tabulata, and Tetracoralla. The origin of 

 these widely differentiated stocks must surely have occurred 

 much earlier in the Ordovician and most probably well back in 

 the Cambrian. 



Probable Ancestry of the Tetracoralla. 

 There are two species of cup or individual Tetracoralla of the 

 Black River faunas so extremely dift'erent in their specialization 

 that they also suggest a long unrecorded history for that sub- 

 class. These are Streptelasma profundum and Lindstroemia 

 zi'hiteavesi. The extremes of variation which they represent 

 are almost as great as may be found between any two members 

 of the sub-class and the problem of distinguishing the more 

 primitive specialization must be attacked in other ways than by 

 a comparison of adult characteristics. 



