LESSONS IN GEOLOGY. 



FiV/t Life, This Devonian system is celebrated for the great 

 development of flab life, which the fowili of the epoch announce. 

 This subject owes much of its completeness to Agassiz, who 

 published, in 1844, a monograph upon the Devonian fish. He 

 ranked the sixty-five British species under his two clasnes, the 

 / and Ganoid, which we have described in a previous 

 lesson. Of the plaooids no entire skeletons are preserved, but 

 their existence ia indicated by the frequent occurrence of fin- 

 spines icltlltyodorulitei and teeth. 



The ganoids comprise the greatest number of these paleozoic 

 fish. Those early seas must have presented a sight indeed 



the restitution of some of these animals is very imaginative, 

 and may be wrong. The shields of the pteriohthys and the 

 eoeoosteus may not represent the full extent of their bodies as 

 they do in the figure. 



The fauna of the period is given by the remains of fact or 

 sea>woeds, some marsh plants of the bulrush species, and sedge 

 (juncitn) ; and of land plants, some bear a resemblance to the 

 lepidodondron and calamites of the carboniferous period. 



The yellow sandstones of Ireland afford some very fine fossils 

 of the Adiantita Hibernieut (Fig. 01). The venation of the 

 leaves is wonderfully preserved. 



strange to us. No reptiles were to be seen, perhaps no birds, 

 but the power of life seemed to have given itself full liberty 

 within their waters, and there swarmed fish of every description, 

 wonderful creations, some entirely encased in enamelled plates, 

 which shone and reflected the glistening sunlight as they shot 

 mth marvellous velocity through the water. These strong plates 

 must have been for some material use, and what other purpose 

 could they serve than for defence ? How powerful the enemy 

 to resist whdm such casements were required ! What desperate 

 encounters what a violent existence do these facts suggest ! 



Besides the Ptcrichthys JUilleri, which has been illustrated 

 in Fig. 21 (Vol. IV., page 61), the following specimens of the 

 fish of the period are figured in the cut accompanying this 

 paper : Cephalaspis Lyelli (Fig. 64) ; Coccosteus cuspidatus 

 (Fig. 65) ; Polypterus (Fig. 66) ; Diplocanthus (Fig. 67). 



Still, with regard to these figures, it is only fair to add 

 that the reader must remember that, although we know more 

 about tho fish of the Devonian age, as a class, than we do 

 of any other class whose records the rocks preserve for us, yet 



TABLE OP FOSSILS OF THE PERIOD. 

 Plants. Calamites, Lepidodendron, Stigmaria, Fuci. 

 Corals. Amplexus, C/tonophyllum, EndophyUum, Favosites, Polymorpha, 



Cyathophyllum, Heliolites porosa, Aulopora, Sponyiophyllum, 



Hallia. 



Polyzoa. Fenestella, Eetepora, Hemitrypa, Ptylopora. 

 Brachiopoda. Athyris, Atrypa, Calceola, Strophomena, Orthis, Penta- 



merus, Producta, Rhynconella, Spirifer, Stringocephalus, Terebrm- 



bulee, Virgo, Uncites, Daindsonia. 

 Conchifera. Avicula, Aviculopecten rugosus, Corbula, Cypricardia, 



Megalcxlon, Nucula, Cucullea. 

 Gasteropoda. Euompbalus, Lozonema Murcbisonia, Natica meridio- 



mills, Pleurotomaria turbo, Vermetus. 

 Pteropoda. Belleropbon, Porcellia. 

 Cephalopoda. Cyrtoccras, Goniatites, Nautilus germanus, Orthooeras, 



Clymenttt. 



Echinodermata. Cyathocrinus, Hexacrinus, Adelocrinus. 

 Cnutacca. Phillipsia, Trimerooepbalus harpes, Pbacops, Pterrgotns. 

 Fish. Acanthodes, Actinolepis, Cephalaspis, Cheiracanthut, C7iiroUpw. 



Coccosteus, Dmdrodus, IKpIocanthiu, Diptenu, Holoptychias, Ott- 



lepis, Polypterue, Platygnathus. Pterichthys, Ptychacoii[h. 



