714 



ARTHROPODA 



PHYLUM YII 



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

 and Wanneria. 



Mesonacis Walcott. Thorax long and tapering, tlie tliird segment enlarged, and 

 tlie 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. 



Elliptocephala Emmons. Like Mesonacis, but 

 without the enlarged third segment, and with long 

 spines on the axial lobes of the last live 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 back of the fifteenth, the great spine of 

 which is iisually 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 



Ringsaker.Norway. Lefriikif öf gTabeiia with broader spines on the pleura of the thoracic 



romoved, exposing hypostoma beneath. 3/. j -.t, • ^^ no, ,i 



(after Holm). ^ '"■ ■ '^ Segments, and with a spme 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. Paradoxidae Emmrich. 



Opisthoparia with large cephalon, small free cheeJcs, 

 long narrow eyes, the palpehral lohes not reaching 

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

 ous segments {seventeen to twenty- 

 three). Pygidium small and 

 simple. Cambrian. 



Paradoxides Brongniart (Figs. 

 1369, 1370). Glabella enlarging 

 toward the front. Middle Cam- 

 brian ; Europe, Eastern North 

 America and Australia. 



Fig. 1368. 

 Holmia kjerulfi Linnarson. 



Carabrian 



Fio. 1369. 

 l'anuloxides l)ohemi(yus Barr. Cam- 

 bnan (Etage C); Ginetz, Bohen.ia. i^,. 



Family 4. Olenidae Burmeister. 



Opisthoparia with short and 

 Wide cephalon, small pygidium, 



Fig. 1370. 



Paradoxides (cf. 

 yoiing of P. inßatns 

 Cor da) = Hydro- 

 ccpludus carens Barr. 

 Cambrian ; Bohemia. 



