GASTROPODA— PLEUROTOMWM. 803 



but faint; whorls appressed below the suture, forming a sub- 

 sutural band. 



Chesapeakean of Atlantic coast. 



628. P. (Surcula) biscatenaria Conrad. (Fig. 1179, <?.) Miocenic. 

 Larger and more robust than preceding, with three strong spirals 



at the ambitus of the whorls, the upper one double, the lower one 

 commonly divided at the suture; interspiral spaces concave; canal 

 curved at the base. 



Chesapeakean of Atlantic coast. 



629. P. (Surcula) engonata Conrad. (Fig. 11 79,/.) Miocenic. 

 Fusiform, with strong nodules on the shoulder angle and concave 



shoulder; nodes not continued as ribs. 

 Chesapeakean (St. Mary's) of Maryland. 



CXCIV. Drillia Gray. 

 Like Pleurotoma in general form but with a short canal ; aper- 

 tural notch gentle. Tertiary-Recent. 



630. D. ostrearum Stearns. Oligocenic-Recent. 

 Fusiform, high-spired, with narrow, concave shoulder bounded 



by a subsutural spiral; ribs numerous, close-set, cancellated by 

 spirals. Length, 16 mm. 



Chipolan beds of Florida; Caloosahatchie (Pliocenic) of Florida; 

 Recent from North Carolina to Yucatan. 



631. D. abundans Conrad. Oligocenic-Recent. 

 Canal about half as long as the spire ; nearly straight ; whorls 



depressed convex, with a subsutural concavity, and a crenulated 

 spiral ; ribs acute, nearly straight. 



Vicksburgian of Mississippi; Caloosahatchie (Pliocenic) of 

 Florida. 



632. D. incilifera (Conrad). (Fig. nyg, f,g.) Miocenic. 

 Shoulder concave, with three strong spirals, the lower covered 



except in body whorl, the upper two noded by incomplete ribs. 

 In the variety angulata Martin the angle is marked by coarse, round 

 regular nodes which appear just above the suture, and the apical 

 angle is broader. In var. distans Conrad, the apical angle is higher, 

 the spire is higher and the nodes elongated downwards. The 

 shell is also less abruptly contracted at the base. 

 Chesapeakean of Atlantic coast. 



