PALEOZOIC TIME — CARBONIC. 719 



The Favosites ended in the Devonian, but related tabulate Corals still 

 exist. 



2. Echinoderms. — Cystoids, one of the early Cambrian types, the simplest 

 of the Crinoid tribe, embryo-like in their want of symmetry, are unknown 

 after the Devonian. Crinoids, also Cambrian, multiply in genera and species 

 through the Silurian and Devonian, appear under a marvelous diversity of 

 forms in the Subcarboniferous period, and then rapidly decline, few appearing 

 in the Permian, and none of the same paleozoic type in after time. The next 

 period, or that commencing the Mesozoic, has more modern forms under the 

 genus Encrinus, closely related to the living Pentacrinus. 



Starfishes commence in the Cambrian, and Echinoids, the higher Echino- 

 derms, in the Silurian. The latter are abundant in the early Carboniferous 

 era, but they do not lose in Paleozoic time their low-grade multiplicate 

 characteristic ; that is, the excessive number of vertical series of plates in 

 the shell. 



3. Molluscoids. — The Brachiopods, earliest Cambrian in origin, the most 

 abundant of all Paleozoic animal life in species, and in individuals under 

 species, had the larger part of the groups, to which they are referred, intro- 

 duced in the Cambrian and Lower Silurian, but were most numerous in 

 genera and species in the Upper Silurian and Devonian. And although of 

 many species and few genera in the Carboniferous and Permian, the type 

 appears to have lost, at the close of the Permian, all the genera then existing 

 excepting four. These are: Lmgula, Crania, Spirifer, and Rliynclionella ; 

 all of these continue into the Mesozoic, showing remarkable adaptability 

 to varying conditions. Further study may subdivide the genera ; but the 

 general fact remains as regards the groups. The early Cambrian Orthis group 

 continued through Paleozoic time, but appears to have ended at its close. 



4. Mollusks. — The tribe of Pteropods — if the species, so referred, rightly 

 belong here — had predominance over other Mollusks in the Early and Middle 

 Cambrian, the species being many and large. They were numerous also in 

 the Lower Silurian ; but they diminish in numbers afterward. Conulariae — 

 of much more uncertain relations — existed in the Upper Cambrian, but had 

 their largest species in the Silurian, Devonian, and Carboniferous. They are 

 rare fossils afterward ; the last known is from the Lias. 



Lamellibranchs and Gastropods, commencing in very small forms during 

 the Early Cambrian, increased slowly in number of genera through the 

 Paleozoic, without reaching a culminant condition in either of their higher 

 divisions. The Cephalopods also culminate after Paleozoic time. One of 

 the early genera, Orthoceras, had species of large size through the whole 

 Paleozoic, and survived until the middle of the Mesozoic. 



5. Limuloids. — Limuloids of Eurypterid type commenced in the Lower 

 Silurian, have species of great size in the Upper Silurian and Devonian, in 

 which era they passed their culmination, and ended with small species in 

 the Carboniferous era. The family of Limulids, a branch from the earlier 



