PELECTPODA 575 



O. lurida Carpenter. The Pacific coast oyster. Diameter 5 cm. or 

 less; shell thin and purplish: Puget Sound to California. 



FAMILY 3. PECTINIDAE. 



Scallops. Shell inequivalve, either free or attached, with radial ribs 

 or striations; foot cylindrical; without siphons: about 7 genera. 



PECTEN 0. F. Miiller. Shell consisting of a round body with radi- 

 ations and 2 wings; hinge line straight and toothless; shell rests on the 

 right valve, which is the less convex and has a prominent notch, where 

 the anterior wing joins the body of the shell; muscle near the middle of 

 the body; gill attached by one lamella only: numerous species. Scal- 

 lops leap and swim by snapping the shell together, giving them a zigzag 

 course; they are used for food, the muscle being usually the only part eaten. 



Key to the species of Pecten here described : 



Oj Valves with about 20 radiating ribs P. IBBADIAIVS 



a a Valves with about 50 ribs P. ISLANDICUS 



o 3 No ribs P. MAGELLANICUS 



P. irradians* Lamarck. Common scallop 

 (Fig. 905). Shell with about 20 radiating ribs 

 and with numerous lines of growth ; wings large 

 and equal in size ; color variable, the upper valve 

 being the darker ; length 75 cm. ; breadth a little 

 less; 30 to 40 bright blue eyes in the edge of 

 each mantle : Cape Cod to Texas, locally farther 

 north ; often abundant among eel grass and over 



vi,q flafc Fig. 905 Pecten irradians 



mud flats. (Verrill). 



P. islandicus (Mill.). Shell with over 50 



narrow ribs; wings unequal in size, length 9 cm.; width 75 mm.: Cape 

 Cod to Arctic Ocean; Europe. 



P. magellanicusf (Gmelin). Giant scallop. Shell without ribs but 

 covered with fine radiating striations, 17 cm. long; wings equal in size; 

 upper valve brown, lower white: New Jersey to Labrador. 



ORDER 4. EULAMELLIBRANCHIATA. 



Two gills on each side (Fig. 890, C), each of which is composed of 

 the filamentous leaflets joined by vascular trabeculae (interfilamentary 

 connections) to form a continuous lamella; each gill composed of 2 

 lamellae, which are the two limbs of the leaflets joined by interlamellar 



* See "Habits and Life History of the Scallop (Pecten irradianft)" by J. Risser, 

 Ann. Com. Fisb., Rbode Island, 1901. 



t See "Habits, etc., of the Giant Scallop," etc., by G. A. Drew, Stud. Univ. of 

 Maine, No. 6, 1906. 



