734 



NORTH AMERICAN INDEX FOSSILS. 



433. T. plebeia Say. (Fig. 1068, d-f.) Miocenic. 



Whorls convex, suture depressed ; spirals numerous. A variety 

 has the whorls flattened (Fig. 1068, e). Another variety, octo- 

 naria, has one strong spiral, the others variable (Fig. 1868,/). 



Chesapeake formation of New Jersey, Maryland, Virginia. 





FlG. 1068. a, Turritella cequistriata ; 6, c, T. indenta ; d-f, T. plebeia. (After 



Martin, Md. Survey. ) 



434. T. variabilis Conrad. (Fig. 1069, a.) Miocenic. 

 Very long and slender, sutures scarcely impressed, four primary 



spirals thick, rounded, in pairs, separated by secondary finer ones. 

 Chesapeake formation of Maryland, Virginia, etc. 



435. T. cumberlandia Conrad. (Figs. 1069, £, and 1070.) 



Miocenic. 

 With two, rarely three, strong spirals and numerous finer ones. 

 Suture closed or depressed. 



Chesapeake of New Jersey, Maryland, etc. 



