266 NORTH AMERICAN INDEX FOSSILS. 



on the sides and with a neck furrow extending entirely across. 

 Eye lobes long, narrow. The many flat pleura (grooved for part 

 of their length) are curved backward and end in spines. Middle 

 Cambric. 



26. P. paradoxoides Matthew. (Fig. 1557,^, /i.) Cambric. 

 Thorax narrow ; pleura short ; axis prominent, with a deep fur- 

 row in each ring; pleura flat, with a diagonal groove ending at 

 base of spine, which is short and bent abruptly backward. 



Middle Cambric of St. John group (Protolenus bed) of New 

 Brunswick. 



XIVA. Bergeronia Matthew. 



This subgenus differs from Protolenus in having the pleura not 

 flat, but strongly bent downward. Middle Cambric. 



27. P. (Bergeronia) elegans Matthew. (Fig. 1557, ^-7n.) Cambric. 

 Cephalon very convex and broad. 



Middle Cambric of St. John group (Protolenus bed) of New 

 Brunswick. 



28. P. (Bergeronia) arcticephalus Matthew. (Fig. 1557, i,;.) 



Cambric. 



Differs from P. elegans in its narrower and proportionally longer 

 and less convex cephalon. 



Middle Cambric of St. John group (Protolenus bed) of New 

 Brunswick. 



XV. Paradoxides Brongniart. 

 Glabella enlarging anteriorly, with well defined lobes, the trans- 

 verse furrows extending entirely across. Eye lobe shorter and 

 farther from the glabella than in Olenellus, with its posterior end 

 farther from the glabella than the anterior. Thorax with 17 to 

 20 free segments; pleura with spiniform extremities. Pygidium 

 a small, plate-like termination of the axis. Middle Cambric. 



29. P. harlani Green. (Figs. 1558, 1559, a, &.) Cambric. 

 Thorax with 17 to 19 segments. 



Middle Cambric, Braintree slates of Massachusetts. 



30. P. lamellatus Hartt. (Fig. 1559, c.) Cambric. 

 Anterior lobe of glabella marked with sharp, transverse lamellae. 



Thorax with 16 segments. 



