PELECYPODA—PRIONODESMACEA. 



503 



Differs from P. jcffersonius in its flat-topped ribs, with about 10 

 radiating striae on each, the flat-bottomed interspaces, and the 

 byssal ear with a few obsolescent rays. 



Very characteristic of the lower Miocenic (Vaqueros formation) 

 of California. 



384. P. (Chlamys) marylandicus Wagner. (Fig. 673, e.) 



Miocenic. 

 ' Distinguished from P. madisonius by its want of elevated ribs ; 

 scales few. 



Maryland (Calvert, Choptank), Virginia, North Carolina. 



385. P. (Chlamys [Lyropecten] ) estrellanus Conrad. (Fig. 

 674, b.) Miocenic. 

 Shell quite convex. Right valve with somewhat square ribs, 



Fig. 674. a, 



Pecten {Lyropecten') magnolia; b, Pecten [Lyropecten) estrellanus. 

 Both X l /z- (After Arnold. ) 



separated by interspaces narrower than the ribs and in each of 

 which is a squarish riblet. Left valve with ribs more rounded, 

 narrower, and with wider interspaces whose riblets are inclined to 

 bifurcation. Both valves marked with radiating lines especially on 

 the anterior and posterior portions. 



