634 ARTHROPODA SUB-KINGDOM VII 
Family 1. Enerinuridae. Linnarsson. 
Cephalon narrow, transverse. Fixed cheeks very large. Free cheeks long, narrow, 
separate, sometimes with a free rostral plate between the anterior extremities. Sutures 
extending from in front of the genal angles obliquely forward, and cutting the anterior 
margin in front of the glabella. Eyes very small or absent. Thorax of from nine to 
A 

Fic. 1317. 
Cephala of Proparia. A, Placoparia. B, Encrinurus. C, Calymmene. D, Diplewra. E, Cheirwrus (Eecop- 
tocheile). F, G, Dalmanites. H, Chasmops. I, Acaste. J, Phacops (after Beecher). 
twelve segments, with ridged pleura. Pygidiuvm generally composed of many segments ; 
limb with strong ribs usually less in number than the annulations of the axis. Ordo- 
vician and Silurian. 
Encrinurus, Emmrich (Cromus, Barr.), (Figs. 1262, 1317, B-1319). Cephalon 
tuberculated ; glabella pyriform, prominent ; 
free cheeks narrow, separated in front by a 
small rostral plate; eyes small, elevated on 
conical prominences ; thoracic segments eleven ; 
pygidium triangular, numerously segmented, 

Fic. 1318. Fic. 1319. limb with fewer ribs. Ordovician and Silurian; 
Encrinurus pune- Encrinurus Bohemicus, Europe and America. 
tutus, Emmr. Sil- Barr. Silurian (Et. E); By poy aes lawl ‘; th fee aA 2 
urian ; Gottland. Lochkow, Bohemia. ! lacopar va, C orda ( 18. 1317, A). Glabella 
more strongly lobed than in Hnerinurus ; eyes 
obsolete ; free cheeks long, narrow ; thorax of twelve segments ; pygidium small, with 
few segments. Ordovician ; Europe. 
Family 2. Calymmenidae. Brongniart. 
Cephalon somewhat wider than long. Fixed cheeks large; genal angles rounded or 
produced into spines. Glabella narrowing anteriorly. Free 
cheeks long, separate, usually with a free plate between the 
anterior extremities. Sutures extending from just in front of 
the genal angles, converging anteriorly, and cutting the margins 
separately. Eyes small, facets nwmerous, visual surface seldom 
preserved. Thorax of thirteen segments, with grooved pleura. 
Pygidium of from six to fourteen segments; axis tapering. 
Ordovician to Devonian: 

Calymmene, Brongt. (Figs. 1317, C, 1320). Body oval in Fie. 1320. 
outline, possessing the power of enrolment to perfection ; — Calymmene senaria, Conrad. 
7 4 ie Me » Ordovician ; Cincinnati, Ohio. 
glabella conical, strongly convex, divided by three pairs of 1), 
deep lateral grooves; eyes small; hypostoma quadrate, 
notched. Thorax of thirteen segments, axial furrows deep; pygidiuin of from six to 
