ORDER III PROPARIA 637 
poited, and usually with more segments than in Phacops. Ordovician and Silurian ; 
Europe. 
Dalmanites, Eminrich (Figs. 1261, 1317, F, G, 13830, 1331). Glabella with three 
well-marked lateral furrows; genal angles produced into 
spines ; eyes large, prominent, and with many distinct facets ; 
pygidium triangular, frequently pointed or mucronated, with 
more than eleven segments, sometimes twenty or more. Ordo- 
vician to Devonian ; Europe, America, and East India. 
Chasmops, M‘Coy (Fig. 1317, H). Differs from Dalmanites 
in having the second pair of glabellar lobes nearly separated 
from the axis, in the obsolescence of the third pair of lobes, 
and in its rounded pygidium. Ordovician ; Europe. 
Vertical Range and Distribution of Trilobites. 
Trilobites are the only large division of the Arthropoda 
which has become extinct. Even in the earliest Cambrian 
they bear evidence of great antiquity,—in their diversified 
- form, larval modifications, polymerous head, and caudal shields. 
These features show that Trilobite phylogeny must extend far 
back into pre-Cambrian times. 
The maximum development of Trilobites occurred in the 
Cambrian and Ordovician, after which they steadily waned 
both in numbers and variety. The genera of the Conocory-  patmaniteslimulu ae 
phidae are wholly restricted to the Cambrian, and here also Green. Silurian; Lockport, 
: Os. nee : pore New York (after Hall). 
are found nearly all the Olenidae and Agnostidae, only scattering 
representatives of which survive into the Ordovician. The Asaphidae are the sole 
remaining family found in the Cambrian, and they are more characteristic of the 
Ordovician and Silurian. 
All families of Trilobites are present in the Ordovician, and continue into the 
Silurian, with the exception of the Conocoryphidae, Agnostidae, and Olenidae, which 
are properly Cambrian types. The Devonian witnesses a decline in the number of 
families present, and with the close of this era, the class practically became extinct, 
since only five genera of one family, the Proétidae, ave met with in the Carboniferous, 
and the single genus Phillipsia alone persists as late as the Permian. 
As regards their geographical distribution, some genera are of cosmopolitan occur- 
rence: such as Agnostus, Conocoryphe, Ptychoparia, Paradoxides, Trinucleus, Asaphus, 
Illaenus, Proétus, Phillipsia, Acidaspis, Lichas, Calymmene, Homalonotus, Chetrurus, 
Phacops, Dalmanites, and others. The majority of forms, however, are extremely 
limited in distribution, so that a large number of genera found in Sweden, Bohemia, 
England, and North America are unknown outside of certain very restricted areas ; 
and the total number of species common to both sides of the Atlantic is very small. 
A remarkable contrast is observable between the older Palaeozoic Trilobites of the 
northern parts of Europe, and those of the middle and southern portions. While the 
majority of northern genera and species are common to Great Britain, Scandinavia, 
and Russia, the forms of the central European provinces (Bohemia, Thuringia, Fichtel- 
berg, the Hartz, Belgium, Brittany, Northern Spain, Portugal, the Pyrenees, the Alps, 
and Sardinia) are so dissimilar as to stand in closer relationships with the North 
American than with the first-named Trilobite fauna. Of the 350 species found in 
Norway and Sweden, and of the 275 in Bohemia, only six are common to both 
provinces, and it is doubtful if these are really identical. 
The first of the accompanying tables shows the range and relative development of 
the orders and the class; the second represents the vertical range of the several 
families of Trilobites. 

Fic. 1331. 
