19 
There are also shown a section of a large specimen of A rieti- 
tes, a mollusk allied to the modem Nautilus and tracks of reptiles 
of the Triassic period, on sandstone from Turner’s Falls, Mass. 
The model of the moon shown in this alcove is described un- 
der Geographic Geology, p. 37. 
Case lA, Hail 35. — Fossils of the Lauren tian period. The 
existence of life at this period has not been definitely proved by 
any remains found as yet. A supposed fossil, Eozdon Canadense, 
is illustrated by several specimens. 
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. 
The remainder of Case 1 and Cases 2A-F.— Fossils of the 
Silurian age or age of Invertebrates. The life of this age is al- 
most wholly marine and made up chiefly of corals, crinoids, 
brachiopods and mullusks. It is illustrated in the collection ac- 
cording to periods as follows : 
Case 1, A and B. — Cambrian and early Silurian fossils. Old- 
hamia — probably a plant of the order of marine algse ; Brachio- 
spongia — a representative of the class of sponges ; Monticulipora 
— of corals. 
Diplograptus, Tetragraptus — Hydroids known as graptolites, 
abundant fossils of this era. The name is derived from the Greek 
word meaning “to write,” and refers to the plume-like nature of 
their remains. Scolithus — supposed to represent the borings and 
tracks of worms. 
Tentaculites — minute mollu.sks of the class of Pteropods. 
Conularia — perhaps also Pteropods. 
Paradoxides, 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 Climatic hnites, are 
shown on a large slab of sandstone from Wisconsin. The num- 
ber of important animal types having existence in even the earl- 
iest geological periods is worthy of note. 
Between Cases i and 2, a cast of an Orthoceras^ nine feet in 
length. This shows the size which these Cephalopods, repre- 
