<24 



.---■'i^^ L. LUGUBRIS 

 ; att£> flfi A I 



(A Mi ZAA^ ,' 



A / 



/A /r^MoA r^n, o ' O 



600 800 1000 1200 1400 1600 1800 2000 Z200 2400 



area; INSCRIBING RECTANGLE OF LEFT VALVE OUTLINE (SQ.MM.) 



100 200 



^0 600 800 1000 1200 1400 1600 1800 2000 2200 2400 



AREA; INSCRIBING RECTANGLE OF LEFT VALVE OUTLINE (SQ.MM.) 



lulran of the Ufha haulms group. Increase in the density of the plicae, number per unit ai 

 '•niihli IT ^r*""' ''™ ""'"■ ■^""- ^' Scattergram of Colorado sample only. Arrows 

 "own by hypothetical regression lines visually filled to plots ot terminal species in group. 



Fk. 2._Evo1, 



masured. from ColoradoT'Ne" 



on left valves of progressively younger species. A. Scattergram for all specimens 

 lower left-hand corner of each graph indicate direction of increasing plication 



