630 ARTHROPODA SUB-KINGDOM vn 



nearly smooth ; free cheeks large ; hypostoma deeply forked ; eyes large and prominent ; 



thoracic segments Bight 



FIG. 1303. 



Megalasp-is extenuata, Ang. Ordo- 

 vician ; East Gottland, Sweden. 1/1 

 (after Angelin). 



broad ; eyes large. 



FIG. 1302. 

 :, Linn. Ordovician ; Pulkowa, near St. Petersburg, Russia (after Salter). 



pygidium not strongly segmented, often nearly smooth. 

 Some species attain a length of 0'6 m. Very profuse in 

 the Ordovician of Europe and North America. 



Sub -genus: Meyalaspis, Angelin (Fig. 1303). Like' 

 Asaphus, but with more defined and cylindrical glabella. 

 Ordovician ; Europe. 



Oyyyia, 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 

 Europe, Asia, and North 

 America. 



Nileus, Dalman. Thoracic 

 segments eight ; axis very 

 Ordovician; Europe. 



FIG. 1305. 



A, Illaenus Dalmani, Volb. Ordovician ; Pulkowa, near 

 St. Petersburg, Russia. Jl, C, I. crassiemula, Dalman. 

 Ordovician ; Dalekarlien, Sweden (after Holm). 



FIG. 1304. 



Ogygia Guettardi, Bro'ng. Or- 

 dovician; Angers, France. 

 Mechanically deformed indi- 

 vidual (after Brongniart). 



Aeylina, Barr. (Fig. 1306). Glabella strongly convex, prominent, smooth; fixed 





