COMPLETE GRAU : PECTINIDAE OF THE EASTERN PACIFIC 137 



convex, with adult ribs (below Chlamys stage) straight or irregularly 

 waved and moderately to heavily imbricated ; ribs actually low ridges on 

 outer surface of valve, no trace of them being visible from interior. 

 Auricles usually having margins obliterated by surrounding shell deposit ; 

 no ctenolium. Left valve flattish and usually slightly smaller than right ; 

 structure of ribs and auricles same as on right valve. Hinge line straight 

 when growth of shell not hampered; when growth is restricted (as in 

 narrow rock crevices), new hinge lines are formed successively lower so 

 valves can continue to open ; in such cases hinge line tapers downward on 

 each side of ligament, more so posteriorly. Color range deep brown to 

 pale brown, the right valve lighter; interior white, occasionally with 

 large and irregular dark-brown central area and often brown along 

 ventral margin ; large purple stain on hinge area. 



Remarks: In the juvenile stage this species is quite constant. Adoles- 

 cent and adult specimens vary greatly in convexity and outline, but are 

 always easily recognizable. Very young specimens bear a strong resem- 

 blance to Chlamys hastata (Sowerby) ; for the distinguishing features 

 see Remarks under that species. 



Geographical range: Aleutian Islands to Magdalena Bay, Lower 

 California, Mexico. Also reported from Guadalupe Island, Mexico, 180 

 miles west of central Lower California. 



Geochronological range: ?Miocene, Pliocene, Pleistocene, Recent. 



Bathymetric range: Low tide to 30 fathoms, possibly deeper. 



Ecological data: Free-swimming juveniles often found on gravel 

 bottoms ; byssal attachment to a fixed object occurs when shell is any- 

 where from 15 to 25 mm. high, cementation beginning soon thereafter; 

 one or more of the following are often commensal on the left valve of 

 adult specimens: hydroids, "worm tubes," barnacles, bn'ozoa, boring 

 sponges. 



Hancock Expeditions Collecting Stations: 

 SOUTHERN CALIFORNIA and SANTA BARBARA ISLANDS: 



63 stations ; shore to 20 fms. 

 WESTERN LOWER CALIFORNIA: 9 stations; 2-30 fms. 



Genus PECTEN Miiller 1776 



Pecten Miiller, 1776, pp. xxxi, 248. Type species: Ostrea maxima 

 Linne, 1758, p. 696; type locality: "Habitat in Oceano Europaeo." 

 [First valid designation as type species: Schmidt, 1818, p. 67.] 

 Geographical range: Andoy Island, Norway, to northwest Africa 

 in Atlantic; Spanish Morocco and Algeria in Mediterranean, 



