630 ARTHROPODA SUB-KINGDOM VII 
nearly smooth ; free cheeks large ; hypostoma deeply forked ; eyes large and prominent ; 

Fic. 1302. 
Asaphus expansus, Linn. Ordovician ; Pulkowa, near St. Petersburg, Russia (after Salter). 
thoracic segments eight; pygidium not strongly segmented, often nearly smooth. 
Some species attain a length of 06 m. Very profuse in 
the Ordovician of Europe and North America. 
Sub-genus: Megalaspis, Augelin (Fig. 1303). Like 
Asaphus, but with more defined and cylindrical glabella. 
Ordovician ; Europe. 
Ogygia, Brongt. (Fig. 1304). Glabella not greatly ex- 
panded, and with four or five lateral furrows ; hypostoma 
pentagonal, with rounded posterior margin ; thoracic seg- 
ments with grooved pleura. 
Ordovician ; Europe. 
Illaenus, Dalman (Figs. 
1288, F, 1305). Cephalic and 
caudal shields large and convex, 
semicircular in outline ; glabella 
smooth, indistinct ; free cheeks 
small; hypostoma convex, ovoid, 
posteriorly notched ;_ thoracic 
segments usually ten, with 
smooth pleura; pygidium 
smooth, with short and incon- 
spicuous axis. Abundant in 
the Ordovician and Silurian of 
Fic. 1303. Europe, Asia, and North 
AMegalaspis extenuata, Ang. Ordo- America. 
moet ss Ura a zm Nileus, Dalman. Thoracic 
segments eight; axis very 
broad ; eyes large.. Ordovician; Europe. 

Fic. 1804. 

BiG. 1805. Ogygia Guettardi, Brong. Or- 
A, Illaenus Dalmani, Volb. Ordovician; Pulkowa, near dovician; Angers, France. 
St. Petersburg, Russia. 3B, C, J. erassicauda, Dalman. Mechanically deformed — indi- 
Ordovician ; Dalekarlien, Sweden (after Holm). vidual (after Brongniart). 
Aeglina, Barr. (Fig. 1306). Glabella strongly convex, prominent, smooth ; fixed 
' 
*. 
a 
