284 Cincinnati Society of Natural History. 
Galena limestone of Illinois, lowa and Wisconsin, belongs to the upper 
part of this group. It is found almost everywhere on the continent 
where Lower Silurian rocks are exposed, and in all cases is very fossil- 
iferous, The distribution of the genera that are first observed in this 
group is as follows: . 
Among the Protista, Beatricea passes up to the Clinton; Pasceolus 
to the Hudson River: and Brachiospongia and Cnemidium are peculiar 
to it. 
Among the Polypi, Aulopora passes up through the Upper Silurian 
and Devonian : Paleophyllum, Protarea and Stellipora to the Hud- 
son River; and Buthograptus is peculiar to it. 
Among the Echinodermata, Agelacrinus passes up to the Subcarbon- 
iferous ; Homocrinus, and Paleaster to the Devonian; Thysanocrinus, 
Petraster, Lecanocrinus, Glyptocrinus, and Dendrocrinus to the Ni- 
agara; Carabocrinus, Cyclocystoides, Heterocrinus, Lichenocrinus, 
Paleasterina, Pleurocystites, Porocrinus, and Retiocrinus to the Hud- 
son River; and Amygdalocystites, Ateleocystites, Cleiocrinus, Co- 
marocystites, Edrioaster, Hybocystites, Schizocrinus, Scyphocrinus, 
Syringocrinus, and Teniaster are peculiar to it. 
Among the Bryozoa, Ptilodictya passes up to the Coal Measures ; 
Alecto, Ceramopora, Clathroporo, and Retepora, to the Devonian ; 
Escharopora, Paleschara, and Phenopora to the Upper Silurian ; 
Bythopora to the Hudson River, and Arthroclema is peculiar to it. 
Among the Brachiopoda, Atrypa and Pholidops pass up to the De- 
vonian; and Zygospira and Rhynchotreta to the Lower Helderberg. 
Among the Pteropoda, Conularia passes up to the Kaskaskia Group 
of the Subcarboniferous, and Zentaculites to the Chemung. 
Among the Gasteropoda, Carinaropsis, Cyclora and Microceras pass 
up into the Hudson River, and Conchopeltis is peculiar to it. 
Among the Cephalopoda, Z'rocholites passes into the Hudson River. 
Among the Lamellibranchiata, Pterinea and Cypricardinia pass up 
to the Carboniferous; Cleidophorus to the Niagara; and Matheria is 
peculiar to it. 
Among the Annelida, Cornulites passes up to the Devonian. 
Among the Crustacea, Calymene and Dalmanites pass up to the De- 
vonian; Acidaspis and Bronteus to the Lower Helderberg; and T'rinu- 
cleus and Sphaerocoryphe to the Hudson River. 
Of the 67 genera thus enumerated as commencing their existence in 
this Group, 19 terminated in the Hudson River, 14 in the Upper Sil-: 
urian, 13 in the Devonian, 5 in the Carboniferous, and the remaining — 
