AETHBOPODA — TRILOBITES. 
85 
to include the genal angles, as in Olemis (Fig. 40 h), Para- 
doxidcs, Triarthrns (Fig. 39), Ogygia, Brontcus, and Addaspis. 
Trilobites with the latter character are called Opisthoparia 24. 
Table-case 
•25. 1 
c 
Pig. 40. — Examples of Trilobites. a. Hypoparia, Agnostus ininceps, Oleni- 
diau Age ; enlarged times, b, Opisthoparia, Oleniis cataractes, 
Olenidian Age. c, Proparia, Staurocepliahis Mnrchisoni, Wenlockian 
Age. 
(back-cheeks), while those with the free cheeks in front only 
are called Proparia (front-cheeks). 
Trilobites are found well developed in the oldest Cambrian 
rocks, being represented by Hypoparia, which soon die out, 
and by Opisthoparia. Three genera of the Opisthoparian 
Family Olenidae, Olenelli(S, Paradooyides, and Olemis, have 
given their names to the Lower, Middle, and Upper Cambrian 
Ages. With the Ordovician arise the Proparia, and the 
Trilobita as a whole attain their acme. Through Silurian 
and Devonian times they gradually decline in numbers and 
size, till in the Carboniferous only a single family remains, 
of which one genus, Philliima, struggles on to the Permian. 
The British trilobites are allied to those of Scandinavia 
and Pussia, rather than to those of Bohemia and the rest 
of Europe and eastern North America. They have been 
described mainly by J. W. Salter and H. Woodward in the 
Monographs of the Palaeontographical Society, and many 
specimens there figured are in the national collection. 
The large Paradoxides from the Middle Cambrian of St. 
Davids will attract notice. Angelina Sedgwicld from the 
Tremadoc Slates is the usual text-book instance of how 
fossils may be distorted by earth-movements. The Lower 
Cambrian Sandstone of Comley, Shropshire, has yielded frag- 
Table-case 
25. 
Wall-case 
14b. 
Table-ease 
24. 
Wall-case 
14a. 
Table-cases 
25, 24. 
