NORTH-CAROLINA GEOLOGICAL SURVEY. 



283 



FIG. 202. 



One of the most common pectens of the white eocene marl, 

 is represented by figure 202. It differs 

 from the P. membranacea in having only 

 about half the number of ribs. The P, 

 membranacea having upwards of eighty, 

 while this has about forty-four. 



An observer cannot fail to perceive the 

 striking difference in the species of pec- 

 tens of the white eocene marl of E"ew- 

 Hanover and Onslow counties, and those of the miocene. 



FIG. 203. 



FIG. 203A. 



PLICATULA MARGINATA. (Fig. 103.) 



Shell strong and thicl^ but rather 

 small; valves sub-equal, ovate, wedge- 

 form, with three strong radiating plicae. 



FAMILY MYTILTDAE. MYTILUS INCRASSATT76. 



(Fig. 203A.) \ 



Shell nacreous, thick, somewhat infla- 

 ted, marked with concentric lines of 

 growth; anterior margin arched ac- 

 cuminate; posterior rounded, some- 

 what dilated ; umbones acute. It 

 is usually much injured by exfolia- 

 tion and rarely perfect. 



FIG. 203B. 



it may 

 ocene. 



CRENELLA. (Fig. 203B.) 



Shell small, short, 

 thin, smooth in the 

 middle ; hinge, mar- 

 gin crenulated behind 

 the ligament. It ap- 

 pears to be rare,though 



be owing to its frailness. Mi- 



