3 
II. KURONIAN ACJE (Upper Azoic; Cambrian). \ 
First appearance of Zoophytes, Worms, and Crustaceans. \ 
Reign of Protozoans continued. 
Period of Pal^eopyge (the sole Crustacean) ; Oldhamia (Hy- 
droid Acaleph) ; Eozoon Bavaricum. 
III. S1LURIAX AGE. 
First appearance of well-preserved Radiates, and, at last, of Ver¬ 
tebrates." 
Reign of MoLLUscs-especially Orthoceratites and Brachiopods (Bi¬ 
valves with central beaks and unequal valves). 
Period of Trilobites; Orthoceratites; Brachiopods; Cysti- 
deans (Crinoids with arms wanting, or central) ; Graptolites (Hy-| 
droid Acalephs) ; Protozoans. I 
Lower Silurian. (Silurien inferieur) 
1. St, John’s Period (Lower Lingula Flags ; Primordial ; Etage 
C). 
First appearance of Trilobites, Brachiopods. 
Reign of Trilobites. 
Period of Paradoxides , Conocephalites, Ariondlus, Microdiscus , Agnos- 
tus (Trilobites) ; Orthis, Lingulella , Piscina * (Brach.) 
2. Potsdam Period, (Upper Lingula Flags and Lower Tremadoc). 
First appearance of Gasteropods. 
Reign of Trilobites continued. 
Period of Olenellus , Conocephalites , Batliyurus , Salterella , (Trilob.); 
Obolus, Obolella, Lingula* Lingulepis, Lingulella, Orthisina, Camerdlay 
(Brach.) ; Archceocyathus (Sponge) ; Scolithus, PalceophycuSy Licro- 
pliyous (Fucoids), in the Lower Potsdam; of Picellocephalus, Ptychas- 
piSy Agnostus and other Trilobites; Pleurotomaria (Gasterop); Orthis, 
Lingula *, Lingulepis (Brach,) in the upper Potsdam. 
3. Calciferous Period, (Probably most of the Taconic; upper 
Tremadoc.) 
First appearance of Tetrabranch Cephalopods, Lamelli- 
branchs, (bivalves with valves equal and beaks not central), Recep- 
taculites. (Foraminifer). 
Reign of Cephalopods, Gasteropods, and Brachiopods. 
Period of Nautilus*, Lituites, Orthoceras (Cephal.); Pleurotomaria, 
Metoptoma (Gaster.) 
4. Levis Period, including Levis proper, Lauzon and Sillery 
(Lower Llandeilo) ; 5 Chazy (Upper Llandeilo) ; 6 Ttenton ; 
7 Nashville (Hudson River : Cincinnati). 
First appearance of Spiriferidae, Rhynchonellidae, Strophomenidae, 
(Brach.) ; Bryozoans ; Cystideans, Crinideans (Fixed Crinoids); 
Echinoids; Graptolites; Zoantharia tabulata; Zoantharia 
rugosa (Corals with conspicuous quaternary lamellae); disappear¬ 
ance of Maclurea ; Olenus , Agnostus, Ogygia , Asaphus ; decline of 
Graptolites. 
Reign of Chambered Molluscs with simple septa ; Gasteropods ; 
Brachiopods; Fixed Crinoids; Zoantharia tabulata (corals with 
well-developecl walls and transverse diaphragms —Hydroid Aca¬ 
lephs of Agassiz) ; Graptolites. 
Period of Trinucleus, Asaphus , Illcenus, Lidias, Calymene, Agnostus , 
Ampyx (Trilob.) ; Cyrtoceras, Cryptoceras , Ormoceras , Lituites, Or¬ 
thoceras, etc. (Tetrabranchs with simple septa) Cyrtolites, Bucania, 
Maclurea, Pleurotomaria , Murchisonia, Holopea, Cyclonema, Eunema, 
Subulites, Metoptoma, (Gasterop.) ; Ambonychia, Ctenodonta, Modiol- 
opsis, Pterinea, Conocardium, Cyrtodonta, (Lamellibranchs) ; Rhyn- 
chonella, Stricklandinia, Zygospira, Orthis, Leptoena, Strophomena, Pis¬ 
cina*, Trematis ( Brach-.); Ptilodictya (Bryozoon); Glyptocrinus, Eet- 
errcrinus, Palmcrinus, etc., with numerous Cystids (Crinoidea) ; 
