502 NORTH AMERICAN INDEX FOSSILS. 



Surface imbricated when mature. 



Maryland (Aquia and Nanjemoy), Alabama (Lignitic). 



UJ. P. (Chlamys) greggi Harris. Eocenic. 



Differs from P. choctavensis in its small number of ribs, and their 

 lack of bifurcation and imbrication. 



Lignitic : Alabama, Georgia. 



378. P. (Chlamys) johnsoni Clark. (Fig. 673, d.) Eocenic. 

 Small. A few ribs implanted at front of shell. 



Maryland, Mississippi. 



379. P. (Chlamys) wahtubbeanus Dall. Eocenic. 

 Differs from P. johnsoni in its fewer ribs (about 14), each with 2 



or 3 imbricated radial striae increasing by bifurcation. 



Claibornian and Jacksonian : Alabama, Mississippi, Louisiana. 



380. P. (Chlamys) perplanus Morton. Eocenic-Oligocenic. 

 Ribs subangular, about 23, with sloping sides and equally wide 



interspaces ; an obsolescent thread on each side of the median 

 keel of each rib ; all crossed by regularly spaced, low lamellae, 

 slightly produced over each rib. Byssal notch conspicuous but 

 not deep. Height 34 mm.; width 35 mm. (about twice the length 

 of the hinge). 



Eocenic : Alabama (Jacksonian), Mississippi. Lower Oligo- 

 cenic : Florida (Vicksburgian). 



381. P. (Chlamys) madisonius Say. (Fig. 673, c.) Miocenic. 

 Whole surface covered with scaly striae ; ribs usually about 16, 



rounded, with about 3 striae on top of each. Upper part of byssal 

 ear with few and coarse radiating stride. Byssal notch one third 

 length of ear. 



New Jersey, Maryland, Virginia, North Carolina. 



382. P. (Chlamys) jeffersonius Say. (Fig. 67$, f.) Miocenic. 

 Differs from P. madisonius in its fewer ribs, with about 6 striae 



on top of each, byssal ear covered with fine uniform and numerous 

 radiating striae, byssal notch barely one eighth the length of the 

 ear. As with many of the Pectens these two species grade into 

 each other. 



Maryland, Virginia, North Carolina. 



383. P. (Chlamys [Lyropecten] ) magnolia Conrad. (Fig. 

 674, a.) Miocenic. 



