DEPARTMENT OF GEOLOGY 
19 
Ptyctodus are Placoids. Paleospondylus is considered an ancient 
lampry. Holoptychius and Palceoniscus give a good idea of 
the general form of the scaled Ganoids and Macropetalichthys, 
Pterichthys, Coccosteus are representative Placoderms. 
Aside from its fishes the Devonian period is noted for the 
appearance of the land plants, such as N europteris and Alethop- 
teris (Ferns), Asterophyllites (Horsetails), Adiantites, etc. 
Dictyophyton is a reticulate Sponge. Both the Honeycomb 
corals, such as Favosites, Michelinia, Alveolites, etc., and the 
Cup corals Heliophyllum, Cyathophyllum, Acervularia, Cysti- 
phyllum, Zaphrentis, Campophyllum, etc., were very abundant 
both as to number of species and individuals. An especially 
large number of species of Favosites, Heliophyllum and Zaph- 
rentis is shown. 
Crinoids were comparatively rare in Devonian times. Cupres- 
socrinus, M egistocrinus and Hypsocrinus represent the class in the 
collections. Reemer aster , Aspidostoma, Ophiura, etc., are Star- 
fishes. Brachiopods reached their greatest development in this 
period and all the typical forms are represented: perhaps the 
most noticeable of these is the winged Spirifer of which many 
species are shown. 
Pelecypods and Gastropods are abundant but exhibit no 
decided changes from the preceding period. 
Cephalopods are represented by Orthoceras, Gomphoceras , 
Gyroceras, etc., as before, but to these is added the Goniatites, 
which is a closely coiled form having the juncture of the septa 
and shell forming a zigzag instead of a straight suture. 
Carboniferous Period or Age of Coal Plants. — Land plants are 
the striking features of this period. They are allied to the four 
modem groups of Ferns, Lycopods, Conifers and Horsetails. 
The Ferns surpassed all others in number. Pecopteris, N eur- 
opteris, Alethopteris, etc., are shown both as single leaflets and 
fronds. Many of these have been preserved in the center of clay 
concretions and are shown in a number which have been broken 
open. 
Lepidodendron and Sigillaria are shown by sections of trunks 
and by impressions of the bark. The size of some of the stumps 
of Sigillaria shown indicates that the original tree must have 
attained a height of, perhaps, 80 or 100 feet. Stigmaria probably 
represents the under water stems of Sigillaria or Lepidodendron. 
These were similar, except in size, to the modern Lycopods, or 
club-mosses. 
