gins stra.ight, their distal ends more roiuided on the left v:lve 

 than on the right; external SGul^ture siinilar on hoth wives, v/ith 

 eighteen to tv/enty prominent rarHal ribs, more or less square on 

 the dorsal half of the shell, broader and more roimded on the ven- 

 tral half, separated bj; narrower interspaces; the ribs and inter- 

 spaces in the ventral half of the shell orna.'.ented v/ith radial 

 rovifs of short, blmit scales, smaller in the interspaces, inconsni- 

 Giious on the dorsal half, reduced to a single row and often ab- 

 sent in the interspaces; submargins so-Jlptured v/ith fine, narrov;, 

 irregularly spaced, squamose radid ribs; auricles broad, the ant- 

 erior longer, with a deep byssal notch, both sculptured v;ith squam- 

 ose radial ribs of irregular width, wider and higher than those on 

 the submargins, on the anterior auricle the ribs wider and the 

 scales more prominent than on the posterior; interior of the shell 

 with paired lirae separa ed by e;:cavated intervals. 



■Pi" ens ions .- A right valve: lat., 7A.5 ram.; al"^., ?4.'!r mm.; 

 diam., 3 mm.; length of hinge, ?3.5 mm. -^ left v«lv8 : lat., 

 35.2 mm.; alt., '^4 mm.; "liam., 8.8 vm.; length of hinge, 24.5 mm. 

 Bemarks . - P. sumple "-S is a coraTion form in the "Bowder; fauna 

 and is one of the most wide-spread of the mid-Tertiary Pectens 

 in the Oaribbean region, having been reported under various names 



from almost all localities where deposits of that age h:^ve been 

 explored. ■'^'he characters are fairly constant, although the degree 



