712 



ARTHROPODA 



PHYLUM Til 



Family 6. Raphiophoridae Angeliu. 



Hijimparia with large trilobed cephalon without brim, small, wide 'pygidium, and 



few thoracic segments. Small free cheeks 

 visible on the dorsal surface. Glabella, 

 produced in front of the cephalon as a spine. 

 Ordoviciaii and Silurian. 



Fin. 1362. 



Ampi/x nasutus 

 (Dalnian). Or- 

 dovieian ; Pul- 

 kowa, Russia. 

 X v.- 



Raphiophorus Angelin. 



Glabella obo- 

 Five 



vate, with an abrupt apical spine, 

 thoracic segments. Europe. 



ylm292/x Dalman (Figs. 1357, J?; 1362, 

 1363). Glabella oval, terminating in a 

 round spine. Six thoracic 

 Europe and North America. 

 Lojichodomas Angelin. Glabellar spine long and prismatic in section. Europe and 

 North America. 



Fig. 1363. 



Ampyx portlocki Barrande. 

 Ordovician (Etage D) ; Leiskow, 

 Bohemia, x i/i (after Barrande). 



segments. 



Order 2. OPISTHOPARIA Beecher. 



Free cheeks generally separate, cdivays bearing the genal angles. Facial sutures 

 extending forward from the posterior part of the cephalon within the genal angles, and 

 cutting the anterior margin separately, or more rarely uniting in front of the glabella. 

 Qompound paired holochroal eyes on free cheeks, and tvell developed in all but the most 

 primitive family. 



The families which are here i')laced under this order lend themselves quite readily 

 to an arrangement based uj^on the characters successively appearing in the ontogeny of 

 any of the higher forms. Thus Sao, Ptychoparia and other genera of the Olenidae 



Fig. 1364. 



Cephala of the Ojns^/tojxiria. A, Atops. B, Conocoryphe. C, Ptychoparia. D, Olenus. E, Asaphus. 

 F, lUaenus. G, Proiitus. H, Goklius. I, Lichas. J, Acidas2ns (after Beecher). 



have first a protaspis stage only comparable in the structure of the cephalon with the 

 genera of the preceding order. Therefore this stage does not enter into consideration 

 in an arrangement of the families of the Opisthoj^aria. In the later stages, however, 

 there is a direct agreement of structure with the lower genera of this order. The 

 nepionic Sao, with two thoracic segments (Fig. 1355, B), has a head structure agi'eeiug 

 in essential features with that in Atops or Conocoryphe (Figs. 1364, A, B). A later 

 nepionic stage, with eight thoracic segments (Fig. 1355, G) agrees closely with the 

 adult Ptychoparia or Olenus (Fig. 1364, C, D). These facts clearly indicate that the 

 family Conocoryphidae should be put at the base of this extensive order. Moreover, 

 as Ptychoparia and Olenus are more primitive and simpler genera than Sao, they, as 



