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 New- 

 Hanover and Onslow counties, and those of the inioceno. 



FIG. 203. 



FIG. 203A. 



PLICATULA MARGINATA. (Fig. 103.) 



Shell strong and thiel^ but rather 

 small; valves sub-equal, ovate, wedge- 

 form, with three strong radiating plicae. 



FAMILY MYTILIDAE. MYTILUS INCRASSATT76. 



(Fig. 203A.) \ 



Shell nacreous, thick, somewhat infla 

 ted, marked with concentric lines of 

 growth ; anterior margin arched ac- 

 cnminate ; posterior rounded, some 

 what dilated ; umbones acute. It 

 is usually much injured by exfolia 

 tion and rarely perfect. 



CRENELLA. (Fig. 203B.) 



Shell small, short, 

 thin, smooth in the 

 T middle; hinge, mar- 



- ;; -.J gin crenulated behind 



sij-2u -^ * to 



the ligament. It ap 

 pears to be rare,though 

 it may be owing to its frailness. Mi 

 ocene. 



