25 
longing 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 pres- 
ent day, they were in Silurian times the most abundant and char- 
acteristic 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. 
Case 2B. — Hudson river and Medina epochs. Brachiopods 
are represented by large slabs containing Leptoena , also many 
species of Lingullela , Lingula and Rhynchonella . Species of the 
two latter genera exist at the present day. They afford a re- 
markable example of the power of a genus to survive the vicissi- 
tudes of time. Glyptocrinus , Iocrinus — Crinoids, the class of 
Echinoderms most abundant in early times. Attached by a joint- 
ed stem and bearing many-branching arms, they have been appro- 
priately termed sea-lilies. 
Arthrophycus — supposed to represent the leathery stems of 
seaweeds. Some authorities, however, regard this fossil as repre- 
senting the markings of worms. 
Case 2C. — Hudson River and Niagara epochs. Eridophyl- 
lum — Corals of the Cyathophylloidae or cup-coral family. Haly- 
sites — Corals of the Halysitidae or chain-coral family. Nearly all 
Silurian corals belong to these two or the Favositid family. 
Streptorhynchus — A representative Brachiopod. Orthoceras 
— many specimens illustrating the size and distribution of this 
Silurian Cephalopod. 
The several sections show that its shell was divided by cross 
partitions into chambers. The animal occupied only the end 
chamber, but a long tube or siphuncle connected the others to its 
body. 
Cases 20 andE. — Niagara and Lower Helderberg periods. 
Favosites, Halysites — Corals. Eucalyptocrinus — Crinoids. Illce- 
nus — Trilobites. Bythotrephis — probably marine Algae. Penta- 
merus — a large and abundant Brachiopod, characteristic of the 
Niagara beds of the Mississippi Basin. Spirifer , Rhynchonella 
