6 NORTH AMERICAN INDEX FOSSILS, 



ing a strong rounded anterior lip; surface with fine longitudinal 

 lines. The ventral side is slightly concave longitudinally, its 

 growth lines nearly transverse. 



Middle Cambric of eastern Massachusetts. 



Fig, 1 215. Hyolithes shaleri, vi'iih sec\\on, (After Walcott. ) 



13. H. neapolis Clarke. (Fig. 12 16.) Devonic. 



Convex side divided into three parts, two flattened marginal 

 areas separated from the median convex area by narrow grooves; 

 this condition is accentuated by compression. Entire surface of 

 shell marked by concentric growth lines only. 



Portage (Naples) of New York. 



II. Orthotheca Novak. 



Differs from Hyolithes in the abrupt truncation of the anterior 

 end; the growth lines are thus uniformly engirdling and do not 

 bend forward upon the dorsal face. Cambric. 



14. 0. emmonsi (Ford). (Fig. 1214,/,^.) Cambric. 

 Shell elongate and slender; apical angle about 8°. Dorsal (?) 



face flattened or slightly concave. The older portion of the tube is 

 septate. 



Lower Cambric of Massachusetts and New York. 



15. 0. cylindrica Grabau. Cambric. 

 Shell small, circular to subcircular in transverse section. Apical 



