ORDER II OPISTHOPARIA 631 
cheeks suppressed ; eyes very large, occupying nearly the whole area of the free 
cheeks ; thoracic segments five or six; pleura 
grooved; pygidium large, with short avis. 
Ordovician ; Europe. 
Family 4. Proétidae. Barrande. 
Cephalon about one-third of the whole animal ; 
genal angles generally produced into spines ; 
glabella tumid, with two lateral basal lobes 
defined by oblique furrows in front of the neck 
segment. ree cheeks large, separate. Sutures 
extending from the posterior margin inward to 
the eyes, and then forward, cutting the anterior Fic. 1306, 
margin separately. Eyes usucll y prominent, often vost Soke ANGE pra fot D); 
large. Thorax of from eight to twenty-two free (after Barrande). } 
segments, with grooved pleura. Pygidium usually 
of many segments; pleural and axial portions strongly grooved; margin entire or 
dentate. Ordovician to Permian. 

Proétus, Steminger (Figs. 1275, 1307). Head-shield semicircular, with thickened 
marginal rim ; glabella well defined, extending nearly to the anterior margin, lateral 
furrows obsolescent, basal lobes often present. Eyes large, 
erescentic, near the glabella; thoracic segments usually ten, 
pleura grooved; pygidium semicircular, margin entire; axis 
elevated, segmented; limb ribbed. Ordovician to Carbon- 
iferous ; common in the Devonian. 
Phillipsia, Portlock (Fig. 1308). Like Proétus, but with 
more prominent glabella, strong basal lobes, and larger, more 
segmented pygidium; thoracic segments nine. This genus 
replaces Proétus in the 
later Palaeozoic hori- 
zons. The last surviv- 
ing species occurs in 
the Permian of North 
America. Maximum 

Fig. 1307. development in Lower 
Proétus Bohemicus, Corda. (15, iferous 
Silurian (Et. E); Konieprus, C arboniferous. 2 Fic. 1308. Fic. 1309. 
Bohemia (after Barrande). Areth USUNM, Barr. Philos: ‘ lif Ladeiietis ROMER 
ys « . hi CPSU JEMMUATETA ATELMUSING LONUNCKt 
(Fig. 1309). Glabella ppin.~ Carboniferous Barr. Ordovician 
f - ‘ ‘ yj Limestone ; Kildare (Et. D); Kuchelberg, 
. o -s o ’ ? - b=) 
about half the total length of head-shield, eee cae Pianien aA, 
contracted toward the front, with oblique 
lateral furrows and basal lobes ; fixed cheeks large ; eyes small, situated at the ends of 
distinct eye-lines from the glabella ; thorax with twenty-two short segments ; pygidium 
small, This is the most primitive genus of the family, and the only one retaining 
archaic eye-lines. The eyes, too, are more distant and forward than in other genera, 
and the number of thoracic segments is larger. Ordovician ; Europe. 
Family 5. Bronteidae. Barrande. 
Dorsal shield broadly elliptical. Cephalon less than one-third the entire length ; 
glabella rapidly expanding in front, with faint indications of lobes. Free cheeks larger 
than the fixed. Facial sutures extending from the posterior margin just behind the eyes 
abruptly inward around the palpebral lobes, and then diverging and cutting the antero- 
