UPPER SILURIAN. 



247 



Characteristic Species. 



1. Upper Llandovery.— Petraia bina Phillips, Atrypa hemispheerica, Rhynchonella. neg- 

 lecta, R. angnstifrcmsS., R. Wilsoni Strophomena arenacea (or concentrica Portl.), S. 

 compressa S., Pentamerus globosus Sow., P. oblongus Sow., Orthislata Sow., Lyrodesma 

 cuneata Phil., Pterinea subkevis M'Coy., Murchisonia angulata Sow., Cyclonema quad- 

 ristriatum, Phil., Raphistoma lenticularis Sow. 



2. Wenlock group. — Petraia bina, Cyathophyllum truncatum Linn., Omphyma tur- 

 binatum (Fig. 477), Favosites Gothlandica, F. alveolar is, Holy sites catenulata, Helio- 

 lites Grayi E. & H., H. interstincta, Syringopora bif areata Lonsd , Cystiphyllum Silur- 

 iense Lonsd. (Fig. 478), Stenopora fibrosa, Ptilodictya scalpellum Lonsd., and many 

 other Bryozoans, Actinocrinus pulcher S., Crotalocrinus rugosus (Fig. 479), Ilypanih- 

 ocrinus de corns Thill., Marsupiocrinus cadntus Phill., Atrypa reticularis, Orthis elegantula, 

 Rhynchonella Wilsoni, Pentamerus galeatus, Strophomena rhomboidalis, Spirifer plica- 

 tellus, Modiolopsis antiqua Sow., Conocardium mquicostatum, Pterinea retroflexa, 

 Grammysia cingulata (Fig. 481), Orthoceras annulatum Sow., Tentaculites ornatus Sow., 

 Acidaspis Barrandii Ketley, Calymene Blumenbachii, Homalonotus delphinocephalus, 

 Lichas Anglkus, Phacops caudatus, Encrimirus variolaris Brngt. The earliest re- 

 mains of Cirripeds yet known occur in the Wenlock limestone. 



o.Ludlow Group. — Graptolithus priodon Bronn., Cyathaxonia Siluriensis M'Coy, 

 Pentamerus Knightii (Fig. 480), Rhynchonella nucula Sow., R. pentagona Sow., Lingula 

 Leicisii Sow., Modiolopsis complanata, Pterinea retroflexa, Avicula, Danbyi M'Coy, Bel- 

 lerophon expansus Sow., Loxonema sinuosum Sow., Conularia subtilis S., Orthoceras 

 bullatum, Calymene Blumenbachii, Encrinurus punctatus Wahl.', Homalonotus Knightii 

 Kbiiig, Lichas Anglicus Beyrich, Phacops caudatus Briinn, several species of Euryp- 

 terus (the earliest in the Upper Ludlow), Pterygotus bilobus (Fig. 482), and other species 

 (one from the Upper Llandovery), Ceratiocaris inomatus M'Coy, C. ellipticus M'Coy. 



Fig. 484. 



Ceratiocaris. 



Salter has illustrated the form of the Ceratiocaris by Fig. 484 : the length is some- 

 times four inches or more. 



In the Ludlow group, mostly its upper part, occur remains of the earliest known fishes 

 of British seas, among which are the species, Onchus tenuistriatus (Fig. 483 c), 

 Plectrodus mirabilis Ag. (Fig. 483 d), (perhaps Cephalaspis), P. pusUbliferus Ag., Pter- 

 aspis Banlcsii Huxley & Salter (Fig. 483 a), Pi. truncatus H. & S., species of Sphagodus. 

 A species of Pteraspis occurs in the Lower Ludlow, and this therefore is the earliest 

 form of fish known. This genus is related to Cephalaspis. There are also in the 

 same rocks Coprolites from some of these Fishes, containing fragments of the shells of 

 the Mollusks and Crinoids on which they fed. Remains of Fishes have also been found 

 in the upper part of the Upper Silurian of Russia and Bohemia. The Pteraspis has 

 been referred to Crustaceans. 



The following tables show the distribution in other countries of some species of the 

 Niagara and Lower Helderberg periods. 



