1'KVONIAN AND OLD RED SANDSTONE SYSTEM U'~> 



survive from the Silurian period, and of the more important genera 

 which make their first appearance in Devonian rocks. 



Among Hydrozoa the Stromatoporoids, which had some 

 representatives in Silurian time, become specially abundant, and 

 are characteristic of Devonian limestones. The principal genera 

 are Stromatopora, Stromatoporella, Actinostroma, Parallelopora, 

 Amphipora, and Stachyodes. 



Among Actinozoa, Acervularia, Alveolites, Arachnophyllum, 

 Cystiphyllum, Pachypora, Favosites, Heliolites, Cyathophyllum, 

 Plasmopora, and Syringopora continue from the Silurian ; and 

 Zaphrentoid corals, which are rare in the Silurian, now become 

 abundant. Calceola, Heliophyllum, and Pleurodictyum occur only 

 in Devonian rocks. Michelinia, Zaphrentis, Mesophyllum, and 

 Phillipsastrea appear and range into the Carboniferous. 



Among Echinoderma the crinoids Cyathocrinus, Ichthyocrinus, 

 and Taxocrinus continue. Ctenocrinus, Cupressocrinus, Hexacrinus, 

 Melocrinus, SpJverocrinus, and Rhipidocrinus are specially Devonian 

 genera. Poteriocrinus and Haplocrinus appear and survive. Of 

 Echinoids certain archaic forms occur, such as Lepidocentrus, which 

 has from five to eleven rows of interambulacral plates. 



Among Crustacea trilobites are on the decline, though indi- 

 viduals are sometimes common. Representatives of twelve genera 

 have been found in British Devonian rocks, Acidaspis, Bronteus, 

 Cheirurus, Cyphaspis, Lichas, Harpes, Homalonotw, Dalmanites, 

 Phacops, Trimerocephalus, Proetus, and Dechenella. Of these Phacops, 

 Proetus, Bronteus, and Cyphaspis are the commonest The species 

 of Dalmanites belong to the section or sub-genus Cryphteus. The 

 Ostracods Beyrichia and Entomis are also common. 



Of Brachiopoda many of the Silurian genera survive and 

 many new forms make their appearance ; of the latter Centronella, 

 Davidsonia, Rensselceria, Megalanteris, Stringocephalus, and Uncites 

 are known in Britain as Devonian fossils only, while Camarophoria, 

 Productus, Strophalosia, and Terebratula (Dielasma) range into tin- 

 Carboniferous. 



Of Lamellibranchia the following Silurian genera occur, but 

 those with an asterisk die out within the period : Ambonyckia* 

 Myalina, Grammysia,* Leptodomus, Ctenodonta, Cardiola* Cleido- 

 phorus* Conocardium, Cyrtodonta,* Nucula. Pterinea is very 

 abundant, and the sub-genus with elongate wings (Actinodesma) is 

 specially characteristic. The following genera appear and range 

 into higher strata: Aviculopecten, Ptychopterta, I'ucitllira, Paral- 

 lelodon, Pleurophorus, Edmondia, Prothyris, Megalodon, Curtonotus, 

 Myophoria (?), and Solenopsis. 



Among (3-astropoda the following genera survive from the 



