20 
The specimens are made up of alternate layers of calcite 
and serpentine, which are thought by some to represent the 
shell and body cavity of an ancient, huge Rhizopod. Others 
regard the masses as of wholly inorganic origin. 
Other interesting Cambrian and Ordovician fossils shown 
are as follows: 
Oldhamia — probably a plant of the order of marine algae; 
Brachiospongia — a representative of the classes of sponges; 
Monticulipora — of corals. 
Diplograptus, Tetragraptus — Hy droids known as grapto- 
lites, abundant fossils of this era. The name is derived from 
the Greek word meaning “to write,” and refers to the plume- 
like nature of the remains. Scolithus — supposed to represent 
the borings and tracks of worms. 
TentacuUtes — Minute mollusks of the class of Pteropods. 
Conularia — perhaps also Pteropods. 
Paradoxidesj Asaphus, Olenellus, Agnostus — Trilobites, the 
most common and characteristic fossils of early Silurian times. 
They were crustaceans, allied to the horse-shoe or king crabs 
of the present day. Two models illustrate the various parts of 
their structure, and tracks of a trilobite, genus Climafichnifes, 
are shown on a large slab of sandstone from Wisconsin. The 
number of important animal types having existence in even the 
earliest geological periods is worthy of note. 
Trenton and Cincinnati epochs. Receptaculites, Selenoides 
— probably calcareous sponges. Favistella — Corals belonging to 
the family Favositidae or honey-comb corals, so called because 
made up of hexagonal, parallel columns. Orthis — a genus of 
the class of Brachiopods, characteristic of this epoch. 
Brachiopods are sometimes called lamp shells, on account 
of their resemblance to a Roman lamp; the two valves of the 
shell are unequal in size, and the beak of the larger curls over 
on that of the smaller. Though found only in small numbers 
at the present day, they were in Silurian times the most abund- 
ant and characteristic form of marine life. In structure they 
have points of alliance with the Worms on the one hand and 
with Mollusks on the other. Pleurotomaria, Murchisonia — 
Gasteropod or univalve Mollusks common in the Trenton 
epoch. 
Hudson River and Niagara epochs. Brachiopods are rep- 
