NORTH-CAROLINA GEOLOGICAL SURVEY. 277 



FAMILY FISSURELLIDAE. KEY-HOLE LIMPETS. 



Shell limpet shaped; some have the margin notched in 

 front ; in others the apex is perforated. Adhere to rocks and 

 stones. 



FISSURELLA REDIMICULA. (Fig. 196.) 



Shell ovate, oblong, elevated, and rather thick; surface or- 

 namented with fine longitudinal ridges, which are intersected 

 by circular lines of growth, which gives the surface a reticu- 

 lated appearance ; margin entire, but ridged internally ; apex 

 truncated, figure inclined, oblong. 



This shell is not an uncommon occupant of the shell marl 

 beds of this State. 



CLASS LAMELIBRANCHIATA. 



FAMILY OSTREIDAE. 



" Shell inequivalve and nearly inequilateral ; free or adhe- 

 rent resting on one valve ; beaks central, straight ligament in- 

 ternal ; muscular impression single and behind the centre ; 

 hinge usually without teeth." 



OSTREA VIRGINIANA. 



Shell thick, strongly and radiately plicated ; concentrically 

 laminated and imbricate ; upper valve nearly flat ; pliated 

 towards the margin ; beaks laterally curved ; very variable. 

 Common in the miocene beds of North- Carolina. 



OSTREA CAROLINENSIS. 



Shell ob-ovate, thick, compressed, concentric lamina imbri- 

 cated, and transversely plaited ; beaks broad and prominent. 

 Fosset large and bounded laterally by strong ridges. 



Occurs in the miocene of North- Carolina, but is less com- 

 mon than the preceding. 



Ostrea radians and O. sellaeformis belong also to the mio- 

 cene beds, together with the Anomia ephippium ; the latter is 

 always broken. 



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