COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 151 



Original description : Pect. testa valde fnaequivalvi, aequilaterali ; 

 auriculis aequalibus; valva [sinistra] planulata sulcato-radiata et 

 striata, altera valde convexa, laevigata, radiatim sulcata, margine 

 ventrali profunde dentato: long. 3.75, lat. 1.5, alt. 3.5 poll. 



Additional description : Shell inequivalve and longer than high ; 

 average fully adult specimen about 110 mm high and 100 mm long; 

 left valve smaller than right and recessed into latter at ventral margin 

 to depth of 6 to 8 mm, hinge line slightly more than half length of disk. 

 Right valve deeply convex; umbo strongly inflated and projecting above 

 hinge margin (starting to do so when shell reaches height of from 35 to 

 40 mm) ; hinge recurved at maturity, with contact surfaces of cardinal 

 crura at right angle to left valve; 19 to 21 rounded ribs, strongly pro- 

 duced ventrally and resulting in prominently dentate margin; inter- 

 spaces about half as wide as ribs; surface of disk covered by very minute 

 growth striae which become stronger near ventral margin. Interior of 

 disk with deep grooves near ventral margin, resulting from external ribs ; 

 reverse surfaces of interspaces flat and ridged. Anterior auricle very 

 slightly longer than posterior; strong convex fold 2 or 3 mm above disk; 

 upper portion of auricle flat, angled at about 45° from perpendicular, 

 finely concentrically lamellose and with 4 or 5 riblets ; byssal notch 

 shallow and ctenolium absent after shell reaches height of 40 to 45 mm. 

 Posterior auricle convex and with 6 to 1 1 faint riblets covered by fine 

 concentric lamellae. Left valve shallowly concave; 18 to 20 rather flat 

 ribs, with 4 or 5 small riblets next to submargins; ribs having one to 

 three grooves near ventral margin ; interspaces slightly wider than ribs, 

 having a low central riblet and being finely concentrically lamellose. 

 Interior of disk grooved near ventral margin as result of external ribs, 

 grooves becoming shallower toward umbonal area; reverse surfaces of 

 interspaces flattened and ridged ; low rounded ridge parallel to sub- 

 margin at base of each auricle and terminating in small white knob at 

 lower end ; cardinal crura prominent and with contact surfaces at right 

 angle to disk. Both auricles concave, concentrically lamellose, and often 

 slightly longer than those of right valve ; 2 or 3 prominent riblets adjoin- 

 ing hinge margin, with occasionally 2 or 3 indistinct riblets below them. 

 Exterior of right valve pale yellow-brown to deep red-brown ; juveniles 

 often purple or lavender, with brown and white blotches and streaks. 

 Left valve medium to deep brown in adult stage, occasionally with 

 purple, lavender, yellow or white maculations on the umbo; juveniles 

 often very brightly colored. Interior of right valve mostly white, with 

 auricles brovioi and disk usually having concentric band of brown or 



