Handbook of Paleontology 313 



scribed for America. Some of the common genera are 

 Dahnanites, Calymene, Illaenus, Lichas, Brontens, Pha- 

 cops, Proetus, Encrinurus. The genera Dicranopeltis, 

 Trochurus, Staurocephalus and Deiphon are especially 

 characteristic. Other crustaceans, especially ostracods, 

 are present. Eurypterids or "sea scorpions" are at the 

 height of their development in the Silurian and many 

 genera occur (Eurypterus, Pterygotus, Stylonurus 

 etc.). They lived in the freshening lagoons of Salina 

 (Upper Silurian) times and became buried in the cal- 

 careous muds (waterlimes) of the shoal waters. The 

 most ancient representative (Hemiaspis) of the horse- 

 shoe crab occurs in the European Silurian. The oldest 

 scorpion (air-breathing animal) is known from Upper 

 Silurian deposits. Other air-breathing animals found in 

 the late Silurian are the thousand-legged worms (myrio- 

 pods). Fishes occur for the first time in basal Silurian 

 formations (Harding sandstone). They are found in 

 Upper Silurian deposits inhabiting fresh-water streams, 

 but they are very rare in America. Sharks of a very 

 primitive character lived in Silurian seas, but very little 

 is known about them. 



Climate. The climate of the Silurian must have been 

 temperate to warm and fairly uniform over the entire 

 world, judging by the varied life and the deposits of lime- 

 stones and dolomites, even in the Arctic regions. The 

 reef-building corals are about the same everywhere, and 

 such characteristic forms as the chain coral {Haly sites) 

 and the honeycomb coral (Favo sites) are similar in all 

 regions, occurring also in the Arctic area. During a por- 

 tion of the period (Salina) an arid or dry climate pre- 

 vailed probably over considerable area. 



