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. 



Deiplion Forbesi, Barr. Silurian 

 (Et. E); St. Iwan, Bohemia (after 

 Barrande). 



FIG. 1327. 



Phacops latifrons, Bronn. 

 vonian; Gerolstein, Eifel 

 District. 



Fio. 1326. 



Phacops Stern if i'ii i, 



Family 4. Phacopidae. Salter. 



FIG. 1325. 



Glabella tumid, ividest in front. Free cheeks con- 

 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. Pygidium 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 

 rounded ; eyes large, prominent ; pleura 

 De- rounded ; pygidium semicircular, margin 



entire. Silurian to Upper Devonian ; Barr. "Devonian (Et. 

 _ , . G) ; Hostin, Bohemia 



Europe 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- 

 Flo . 1329 . ' ian ; Europe and North 



FIG. 1330. America. 



Dalmanites socialis, Barr. Ordovician (Et. D) 

 Wesela, near Prague, Bohemia. Cephalon, 1/1- 



FIG. 1328. 



Pterygometopus sderops, 

 I) aim. Ordovician ; 

 Jswos, Esthonia (after 

 Schmidt). 



Acaste Downinrjiae, 

 Murch. Silurian ; Ludlow, 

 England (after Salter). 



Glabella slightly enlarging, with distinct lateral 



A caste, Goldf. 

 (Figs. 1317, /, 1329). 

 furrows ; pygidium often 



