SUBCLASS I 



TRILOBITA 



719 



Äsaphellus Callaway. Similar to Megalaspis, but with loiiger and flatter glabella, 

 and shorter sbields. Treniadoc ; Europe. Lower Ordovician ; Nortli America. 



Hemigyraspis Eaymond. Similar to Äsaphellus^ but witli facial sutiire marginal 

 in front. Tremadoc ; Eiiroi^e. Lower Ordovician ; North America. 



Symphysurus Goldfuss. Cephalon and pygidium short, sub-hemisplierical, without 

 concave border. Axial lobe narrow. Lower Ordovician ; Europe and America. 



Nileus Dalman. Similar to Symphysurus, but with broad axial lobe and very 

 large eyes. Ordovician ; Europe and North America. 



Subfamily B. Asaphinae Raymond. 

 Asaphidae with hypostoma bifurcated. 

 Äsaphus Brongniart (Figs. 1364, E ; 1384). Cephalon and pygidium short and 



Fig. 1384. 

 Asaphus expansus (Linn.). Ordovician ; Pulkowa, near St. Petersburg, Russia. i/i (after Salter). 



wide, glabella prominent, expanding forward, and reaching 

 the anterior margin, which is without concave border. 

 Axial lobe of pygidium ringed, pleural lobes smooth. 

 Ordovician ; Europe and Asia. 



Onchometopus Schmidt. Similar to Asaphus^ but the 

 glabella only obscurely defined, axial lobe rather wide, and 

 pygidium smooth. Ordovician ; Europe and North America. 



Basüicus Salter. Pygidium strongly ribbed, glabella 

 convex, prominent, facial suture marginal in front. Ordo- 

 vician ; Europe and North America. 



Ogygites Tromelin and Lebesconte {Ogygia Brongniart) 

 (Fig. 1385). Similar to Basüicus, but glabella less pro- 

 minent, and sutures meeting in a point in front of glabella. 

 Ordovician ; Europe and North America. 



Ptychopyge Angelin. Glabella short, facial sutures well 

 inside the margin, pygidium not ribbed, concave borders 

 wide, and doublure very broad. Ordovician ; Europe. 



Isotelus Dekay. Cephalon and pygidium smooth, with 

 wide depressed borders. Axial lobe of thorax wide. Ordo- 

 vician ; rare in Europe, abundant in North America. 



Family 12. lUaenidae Corda. 



Opisthoparia with large, convex cephalic and abdominal 

 shields which are nearly smooth and without concave border. 

 Epistomal plate large, hypostoma convex, ovoid. Thorax of 

 eight to ten segmeiits, with smooth pleura. Pygidium smooth, Fcc 13S5. 



with short axial lobe. Ordovician and Silurian. Ogypitcs guettanU (Hrong.). 



Ordovician ; An^«'rs, France. 



Illaenus Dalman (Figs. 1364, F ; 1386). Axial lobe SrJÄBroSrt). ""'" 



