SÜBCLASS I 



TRILOBITA 



723 



r 



K Äncryopyge Clarke. Margin of pygidium with twelve very long, slender, curved 



B: spines. Devonian ; North America. 



H Selenopeltis Corda. Thorax with very long spines extending from the pleura ; 



B pygidium aspinose. Ordovician ; Europe. 



B Glaphurus Raymond. Thorax witli twelve Segments. Pygidium very small and 



B aspinose. Ordovician ; North America. 



Order 3. PROPARIA Beecher. 



Free cheehs not hearing the genal angles. Facial sutures extending from the lateral 

 margins of the cephalon in front of the genal angles, inward and forward, cutting the 

 anterior margin separately, or uniting in front of the glahella. Compound paired eyes 

 scarcely developed or sometimes ahsent in the most primitive family ; ivell developed and 

 schizochroal in the highest family. 



This is the only order of Trilobites which apparently begins during the known 

 Paleozoic, and unlike the other Orders, had no pre-Cambrian existence. The earliest 



Pio. 1398. 



Cephala of the Proparia. A, Placopai'ia. B, Encrinurus. C, Calymene. D, Dipleura. E, Cheirurus. 

 F, Dahnanitina. G, Dalmanites. H, Chasmops, I, Phacopidella. J, Phacops (after Beecher). 



forms of Proparia were initiated at the close of the Cambrian and dawn of the 

 Ordovician. The greatest generic differentiation of the group was early attained ; 

 during the Silurian and Devonian a rapid decline ensued, and only one or two 

 genera survived into the beginning of the Carboniferous. 



Among the Opisthoparia, it seems clear that the Conocoryphidae formed the 

 natural base or most primitive family in the order, and is distinguished by the 

 narrow marginal free cheeks and absence of well-developed eyes. It is of great 

 interest and importance to be able to note that und er the Proparia there is a similar 

 primitive family having characters in common with the other, but still clearly 

 belonging to the higher order. Placoparia, Areia and Dindymene constitute a group 

 of apparently blind Trilobites with narrow marginal free cheeks, and present in 

 general the appearance of Atops, Gonocoryphe, Gtenocephalus, and other members of the 

 Conocoryphidae. 



Family 1. Encrinuridae Angelin. 



Proparia with narrow free cheeks ; either blind^ or ivith small eyes. Pygidium 

 composed of many segments, the pleural ribs usually less in numher than the rings on the 

 axial lohe, and usually ending in spines. Ordovician and Silurian. 



Encrinurus Emmrich {Oromus Barrande) (Figs. 1338, B, G ; 1398, B ; 1399, 1400). 

 Cephalon tuberculated, glabella prominent, free cheeks separated in front by a small 



