364 



ARTHROPODA. 



Fig. 219. Harpes 

 ungula, from the 



Upper Silurian of genal angles produced 



(After , ,,, ,, . . -, 



glabella shows the lateral 



Boheinia. 



gin or "limb" perforated by pores (fig. 219). The glabella 

 is conical, the eyes small and of few facets. There are 

 twenty-five or twenty-six thoracic segments, 

 the pleurae are grooved, and the pygidium is 

 extremely small. The only genus of the 

 family is Harpes itself, which is character- 

 istic of the Lower and Upper Silurian. 



2. EEMOPLEUEID^E. In this family the head 

 is greatly developed, semicircular in shape, the 



into spines. The 



OVtJOj ctil(J. LllC' 



facial sutures unite in front of it. The eyes 

 are very long and are reticulated. There are eleven body- 

 rings, with grooved pleurse, and the pygidium is very small, 

 and is often reduced to two segments. This 

 family contains only the single genus Remo- 

 pleurides (fig. 220), which is confined to the 

 Silurian period, occurring in both the Lower 

 and Upper divisions of this formation. 



3. PAEADOXID^E or OLENID^E. Head-shield 

 well developed, crescentic, the genal angles 

 produced. The glabella typically widest 

 anteriorly, with well-marked grooves. The 

 facial sutures nearly parallel, cutting the 

 head-shield separately ; the eyes large. The 

 body is very long (fig. 221, a); the thorax 

 has from twelve to twenty segments, with 

 grooved pleurae ; the pygidium being usually small and of 

 few segments. The family is essentially characteristic of the 

 Upper Cambrian. 



The principal genus of this group is Paradoxides itself (fig. 

 221, a, and fig. 222), with its long and trilobed body, some- 

 times reaching a length of two feet or more. The thorax in 

 this genus is greatly elongated, and consists of sixteen or 

 twenty rings, while the axis of the pygidium often contains 

 two segments only. The eyes are long, reniform, and smooth. 

 The genus is characteristic of the " Primordial " or Upper 

 Cambrian. Plutonia and Anopolenus, with a similar geological 

 range, are closely related to Paradoxides; but the former of 



Fig. 220. Remo- 

 pleurides radians. Up- 

 per Silurian. (After 

 Earrande.) 



