NORTH AMERICAN INDEX FOSSILS. 



4. H. princeps Billings. (Fig. 1212.) Cambric. 

 Apical angle 13° to 15°. Dorsal side flat to slightly convex 



produced anteriorly into a rounded lip. Ventral face varying from 

 uniformly convex transversely to asymmetrical. 



Lower Cambric of Newfoundland and Massachusetts. 



5. H. quadricostatus Shaler and Foerste. (Fig. 1213, oh-c.) Cambric. 



^ ! 



Fig 



[213. a-c, Hyolithes quadricostatus ; e-g, H. terranovicus ; d, 

 operculum. (After Walcott. ) 



Apical angle about 17°. Shell four-sided, the dorsal side broad, 

 flat or slightly concave along the median line. 



Lower Cambric of Newfoundland and Massachusetts. 



6. H. similis Walcott. (Fig. 12 11, /-w.) Cambric. 

 Transverse section subtriangular ; ventral angle sharp. Shell 



wall thin. Ventral face with four raised lines on each side of 

 median angle and between the raised lines are fine longitudinal 

 striae. Differs from H. americaniis in the presence of the longi- 

 tudinal striae, and the smaller apical angle. 



Lower Cambric of Conception Bay, Newfoundland. 



7. H. communis BiUings. (Fig. 121 1, o-q.) Cambric. 

 Nearly cylindrical, except for slight flattening on one side. 

 Lower Cambric, Newfoundland to New York. 



8. H. terranovicus Walcott. (Fig. 12 13, J-^.) Cambric. 

 Transverse section subtriangular or semielliptical. Dorsal face 



