62 Perner & Kodym — Zonal Division and 



In the normal E 2 there are three chief horizons which 

 are recognizable in the entire Silurian area, as follows : 



1. Cephalopod horizon. 15 



2. Brachiopod horizon. 



3. Crinoid horizon. 



Between them can be distinguished several subordinate 

 zones, which in one locality, where the exposure can be 

 described in detail, can be characterized by their fauna ; 

 but in another, not far distant, can not be demonstrated. 

 A majority of the E 2 fossils occur in all the E 2 beds ; 

 some species, however, very characteristic for one limited 

 locality, are totally unknown in others. A detailed 

 scheme of sequence applicable to the whole horizontal 

 extent of E 2 can not be given at present, but I hope future 

 detailed comparative studies of numerous exposures, like 

 those of Kiaer made in Norway's Silurian, will throw 

 more light on this subject. 



Cephalopod Limestones, 



These are usually grayish or bluish, compact limestones, 

 in thick beds, that in some localities have intercalations 

 of brown shales and shaly limestones. Abundant species 

 are : Orthoceras nobile, 0. bohemicum, 0. janus, 0. explana- 

 tum, Cyrtoceras murchisoni, C. vemum, Gomphoceras 

 cylindricum, and Liluites (Ophidioceras) simplex. This 

 horizon is also the chief source of other well known fossils 

 at Dlouha Hora and Hopanina, among them being Cromus 

 beaumonti, Calymene baylei, Harpes ungula, Cyphaspis 

 burmeisteri, C. depressa, Cheirurus insignis, Proetus 

 striatus, Lytospira subuloidea, Murchisonia latona, Lox- 

 onema beraunense, Cardiola bohemica, C. interrupta, C. 

 grandis, Dualina excisa, and Atrypa sappho. A charac- 

 teristic graptolite is the rare Monograptus transgrediens 

 Per. 



Brachiopod Horizon, 



White-gray limestones without shaly intercalations 

 (Dlouha Hora), or dark, thinly bedded limestones alter- 



15 These designations do not mean that, for instance, cephalopods in E 2 are 

 confined to the lowest beds; they are intended only to indicate the sudden 

 and striking appearance of the three groups of animals, so that the sequence 

 named above would mean rather a sequence of different bionomic conditions. 



