194 THE CANADIAN NATURALIST. [Vol. vi. 



tail, will then be found to be most close and intimate with the 

 first phases of the third fauna (Upper Silurian), so that palaeon- 

 tologically the colonies must be regarded as truly Upper Silurian. 

 This result will be brought out by a comparison of the fauna of 

 the colonies with that of the Lower and Upper Silurian periods 

 respectively : — 



A. Specific connexions hetwee/i the Colonies and the Second 

 Fauna. — As yet only two colonies are known in which there is 

 any intermixture of the characteristic forms of the second fauna 

 (Lower Silurian) with those of the colonial fauna, i.e. with those 

 of the third fauna (Upper Silurian). Thus, out of seventeen 

 species in the colony Zippe, there are four species representing the 

 second fauna, with twelve species belonging to the third fauna. 

 On the other hand, in the colony d'Archiac there are only two 

 species of the third fauna (viz. Cardiola interrupta and Grapto- 

 lites p)Tiodon f). It is quite clear, therefore, that the colonial 

 fauna, as a whole, has very slight connexion with the second or 

 Lower Silurian fauna. 



B. Specific connexions between the Colonies and the Third 

 Fauna. — In showing the specific connexions between the colonies 

 and the third or Upper Silurian fauna, it will be advisable to 

 review briefly the difierent orders of fossils represented in the 

 Silurian basin of Bohemia. 



a. Fishes. — No traces of fishes have been detected in the colo- 

 nies or in the whole of the Lower Silurian series, and their only 

 indubitable remains occur in Etages F and G, which have hardly 

 any connexion with the colonies. (Altogether five fishes have 

 been discovered in the Upper Silurians of Bohemia, viz. Coccos- 

 teus primus, C. Agassizi, Asterolepis Bohemicus, Gompholepis 

 Panderi, and Ctenacanthus Bohemicus.^ 



h. Crustaceans. — These are principally trilobites. The trilo- 

 bites of the colonies, not taking into account the four species of 

 the second fauna, are referable to eight species and seven genera, 

 all belonging to the third fauna. The trilobites are, therefore, 

 very limited in number, and their paucity agrees perfectly with 

 the small number of these crustaceans in the first phase of the 

 third fauna, i. c. in e 1, in which only fifteen species are known. 

 On the other hand d 5 and d 4 have together furnished about 

 eighty trilobites peculiar to the last phases of the second fauna. 

 The remaining Crustaceans of the colonial fauna are Pterygotus 

 Bohemicus^ Ceratiocaris incequalisj Entomis migrans, and Apty- 



