636 ARTHROPODA SUB-KINGDOM VII 
lateral furrows, the posterior one cutting off sub-circular basal lobes. Eyes small ; 
thoracic segments ten, with smooth convex pleura; 
pygidium smaller than head-shield, composed of three 
segments, free at their ends. Ordovician and Silurian ; 
Europe and North America. 
Deiphon, Barr. (Fig. 1325). Glabella globular, without 
lateral furrows; free cheeks minute; fixed cheeks pro- 
duced at either side into a long curved spine. Eyes 
small, situated at the base of the spiniform fixed cheeks ; 
thoracic segments nine, with free spiniform pleura ; 
pygidium short, giving off two pairs of curved spinous 
processes. Silurian ; Europe. 

Family 4. Phacopidae. Salter. 
Fic. 1325. $ 
Deiphon Forbesi, Barr. Silurian Glabella tumid, widest in front. Free cheeks con- 
(Et. E); St. Iwan, Bohemia (after ,. 5 : . 
Barrande). tinuous, united anteriorly. Suture 
extending from in front of the genal 
angles inward to the eyes, and thence forward around the glabella. 
Eyes generally large, always with distinct facets, schizochroal. Thorax 
of eleven segments, with grooved pleura. Pygidiwm usually large and 
of many segments ; limb ribbed ; margin 
entire or dentate. Ordovician to 
Devonian. 
Phacops, Emmrich (Figs. 1317, J, 
1326, 1327). Glabella very wide and 
rounded in front, the two anterior pairs 
of lateral furrows inconspicuous or 
obsolete; genal angles short, generally 
Fic. 1327. rounded ; eyes large, prominent ; pleura 
Phacops latifrons, Bronn. De- rounded ; pygidiwn semicircular, margin 
vonian; Gerolstein, Hifel 

Fic. 1326. 
Phacops  Sternbergi, 
istri entire. Silurian to Upper Devonian ; Barr. Devonian (Et. 
District. : s) = “Host vein’ 
Buvove hat ee G); ostin, Bohemia 
urope and America. (after Barrande). 
-  ‘Trimerocephalus, M‘Coy.  Glabella tumid in front, lateral 
furrows faint or wanting except the basal one; fixed cheeks large; free cheeks forming 
a narrow anterior rim ; 
eyes small, with a few 
large facets ; pygidium 
small. Silurian and 
Devonian ; Europe. 
Pterygometopus, 
Schmidt (Fig. 1328). 
Cephalon obtusely an- 
gular in front; glabella 
enlarging anteriorly, 
lateral furrows well 
defined ; pygidium as 
in Phacops. Ordovic- 
jan; Europe and North 

Fic. 1328. 
Pterygometopus sclerops, 
Dalm. Ordovician ; 
Jswos, Esthonia (after 
Schmidt). 

.Fic. 1329. 
Acaste Downingiae, Fig. 1330. America. 
Murch. Silurian; Ludlow, Dalmanites socialis, Barr. Ordovician (Et. D); 1 d 
, ’ ; “ ’ Ste 
England (after Salter). Wesela, near Prague, Bohemia. Cephalon, 1/;. Acaste, Goldt 
(Figs. 1317, J, 1329). 
Glabella slightly enlarging, with distinct lateral furrows; pygidium often 
