262 



NORTH AMERICAN INDEX FOSSILS. 



IX. Bathynotus Hall. 



Axis wide. Free cheeks united in front and extending back- 

 ward in long genal spines. Thoracic segments 13. Lower Cambric. 



17. B. holopyga Hall. (Fig. 1554.) Cambric. 



Width of cephalon about twice its greatest length. Axis twice 

 the width of the pleural segments. The lower pleural segments 

 bend abruptly downward and end in spines; the last pair is much 

 prolonged beyond the small, subcircular pygidium. 



Lower Cambric (Georgian) of Vermont. 





X. Olenellus Hall. 



Glabella not enlarging anteriorly, marked with transverse fur- 

 rows of which the basal ones at least extend entirely across. Eye 

 lobes longer and nearer the glabella than in Paradoxides, with both 



Fig. 1555. a, b, Olenellus thompsoni, complete individual, X /^> ^^^ young 

 cephalon ; c-e, O. gilberti^ small individual, X /^ > ^"^ two views of larger cephalon, 

 X >^ ; /, Mesonaces vermontana, complete individual, X }4.- (AH after Walcott. ) 



ends practically reaching the glabella. Thorax with 14 segments, 

 with third segment the largest. Pleural grooves shallower, broader 

 and less oblique than in Paradoxides. Pygidium ( ?) a long, telson- 



