802 



NORTH AMERICAN INDEX FOSSILS. 



Chipolan beds of the Gulf States ; Chesapeakean of Maryland. 

 626. P. (Hemipleurotoma) communis Conrad. (Fig. 1179, b, c.) 



Miocenic. 

 Whorls divided midway by a strong, slender carina which bears 



Fig. 1 179. a, Pleurotoma {Hemipleurotoma) albida ; b, c, P. (£?■) communis ; 

 a 7 , P. {Surcula) marylandica ; e, P. (S.) biscatenaria ; f, Drillia incilifera ; g, D. 

 incilifera-distans ; k, D. limatula ; i % Mangilia parva ; J, Surcula engonata. 



the notch ; surface on either side flat or concave ; a second stronger 

 spiral just at or above the suture, and a third below this on the 

 body whorl ; canal less than half the length of the shell. In 

 variety proto communis Martin (Fig. 1179, c), additional interca- 

 lated spirals occur. 



Chesapeakean of Atlantic coast. 

 627. P. (Surcula) marylandica Conrad. (Fig. 1179,0?.) Miocenic. 



Slender, with attenuated canal ; deep reentrant shown by growth 

 lines on shoulder which is concave but not limited by an angula- 

 tion, the whorls being regularly rounded below ; growth lines lamel- 

 lose at intervals, giving a rib-like appearance; spirals numerous 



