714 



ARTHROPODA 



PHYLUM VII 



Cambrian Paradoxides is thought to have been descended from Callavia, through Holmia 

 and Wanneria. 



Mesonacis Walcott. Tliorax long and tapering, the third segment enlarged, and 

 the pleura extended as long spines. The fifteenth segment has a large spine on the 



axial lobe. Ten segments behind the great spine. 

 Europe and North America. 



Ellvptocephala Emmons. Like Mesonacis, but 

 without the enlarged third segment, and with long 

 spines on the axial lobes of the last five segments. 

 Eastern North America. E. asaphoides Emmons. 



Paedeumias Walcott. Like Mesonacis, but 

 with rudimentary thoracic segments and pygidium 

 posterior to the fifteenth segment. North America. 

 Olenellus Hall. Like Mesonacis, but without 

 segments liack of the fifteenth, the great spine of 

 which is usually considered as a pygidium. 

 Europe and North America. 



Olenelloides Peach. Adult is essentially like a 

 larval form of Olenellus, as indicated by the large 

 cephalon and narrow thorax. Europe. 



Holmia Matthew (Fig. 1368). Thorax with 

 sixteen segments, the pleura of which end in 

 rounded spines. Europe and America. 



Wanneria Walcott. Similar to Holmia, but 

 with l^roader spines on the pleura of the thoracic 

 segments, and with a spine on the fifteenth seg- 

 ment. North America. 

 Callavia Matthew. Similar to Holmia, but 

 with narrower glabella, and broader spines on the 

 pleura of the thoracic segments. Europe and 

 North America. 



Peachella Walcott. Cephalon with blunt, tumid 

 genal spines ; elongate, narrow glabella ; small eyes 

 and marked convexity. Eastern Nevada. 



Family 3. P aradoxidae Emmrich. 



Opisthoimria loith large cephalon, small free cheeks, 

 long narroiv eyes, the palpebral lobes not reaching 

 the glabella in the adult. Thorax long, with numer- 

 ous segments {seventeen to twenty- 

 three). Pygidium small and 

 simple. Cambrian. 



Holmia Vjenilfi Linuarson. Cambrian ; 

 Ringsaker, Norway. Left half of glabella 

 removed, exposing hypostoma beneath, s/^ 

 (after Holm). 



Paradoxides Brongniart (Figs. 

 1369, 1370). Glabella enlarging 

 toAvard the front. Middle Cam- 

 brian ; Europe, Eastern North 

 America and Australia. 



Fio. 1370. 



Family 4. Olenidae Bunneister. Paradoxides (cf. 



„ ,„„, young of P. r«:/?af"x 



Ornsthoparia xoith short and Corda.) = Hydr,,- 



Paradoxides hohemicus Barr. Cam- . ■, , , ,, -,• cevhalus cami'< Barr. 



l)rian (Etagc C) ; Ginetz, Bohemia, i/a- '"'*'*^ cephalon, small pygidtum, Cambrian ; Bohemia. 



