120 



ivi.nn a coiimioii acute base, (lividefroqucntlx', and are at inter- 

 vals united again by transverse dissepiments. The outer sur- 

 faces of the branches are striated; the inner bearhydrothec^ie, 

 although these are seldom seen in the flattened specimens. 



Dictvonp:ma hamiltonle ('.'). Hall. (Fig. 1.) (Cana- 

 dian Organic Remains, Decade II.. 18(3."), j). 58. named l)ut 

 not described. ) 



Distinguishing Characters." — Irregularly branching. 

 Branches freely anastomosing, and uniting by transverse 



thin dissepiments. Fen- 

 estrules irregular, elon- 

 gate, and greatly vary- 

 ing in size. Surface 

 roughly striate. 



A specimen ( Fig. 1 ) 

 was taken from the 

 Idlewood Cliff, by Dr. 

 U. T. .1 ackson. It 

 pr()bal)ly came from 



Fig. 1. Dictijonema hamUtonioe Ct) Idlewood Cliff, flip H^Tilotiiffi l>»j(lki 

 Natural size and a portion enlarged four diameters. ^^^^ aiiiwuiLC «7cur«. 

 Stud. Pal. Col. Harvard Univ. Cat. No. 230. (Original.) ^i;i other SDCCi men W-aS 



obtained from the first South Shore Cliff, ]ii-obably from the 

 same beds. 



Class A^thozoa. Fhrenberg. 



The Antliozoa or coral polyps are marine animals ranging from low 

 water to 300 and sometimes even 1,500 fathoms (Zittel). Both simple 

 and colonial forms occur, the latter predominating at the present time, 

 while the former were especially abundant in Palaeozoic time. The 

 ' ' Rugose corals " or Tetracoralla, are the best represented among the 

 fossils, commonly occurring as simple forms, though compound "heads" 

 are by no means uncommon. 



The simple Rugose corallum is well represented by the little St)-eptel- 

 asma rectum (Fig. 2), common throughout the Hamilton shales. It con- 

 sists of numerous radiating septa, disposed in several cycles, and united 

 round their outer margins by a wall or tlieca {psendotheea). This is 

 formed by the lateral expansion or thickening of the septa in that region. 

 The exothecal prolongations of the septa are visible on the exterior of the 



* The description here given applies only to the specimen illustrated. It is provisionally 

 referred to Hall's species ; the tinal determination must await the description of the type 

 specimens of that species. As the above name has been adopted in the literature, it seems 

 undesirable to replace it by another. 



