- 355 - 



stronger hinge; these differences are, hov/ever, slip-ht and v/hen 

 thej? fail the crenu^ati'" ' ~ ' " ^:l:e inner margin of paupers viio . 

 which on young valves is xi.sually more prominent than on adults, 

 serve as an infallible criterior for separation. 



P. radians (Gonracl) (1), v/hich ranges from the Duplin I.Iio- 



fl). Trans. Amer, Assoc. Eat. and Geol., vol. 1, p. 110, 1840; 

 Tuomey and Holmes Pleioc. Pos. 3. Oar., p. 57, pi. 13, 

 figs. 4, 5, 1857 (as Luc ina radians ) . 



cene to the Recent, is very closely related, hut is in general 

 slightly more convex, not as v/ide nor as compressed toward the 

 margins, with a relatively long, sloping anterior dorsal margin, 

 which rather abruptly joins the lateral ::;argin, a no"r'e ronnded 

 posterior margin, hig>ier narror/er and more strongly gyrate umbones, 

 stronger sculpture and a decidedly heavier hinge. 



Occurrence.- lower ?:ioGene : Bowden beds, Bowden, Jamaica 

 (Guppy, and Dall, 1896; Dal.l, 1903). 



