PELECYPODA 



575 



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

 less; shell thin and purplish: Puget Sound to Califoi 



•rnia. 



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. Mailer. 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 eal;en. 

 Key to the species of Pecten here described : 



Oa Valves with about 20 radiating ribs. P irradiavs 



a. Valves with about 50 ribs .' ." ;p^ islandicus 



«^ ^« ''^^ P. MAGELLANICUS 



P. irradians* Lamarck. Common scallop 



(Fig. 905). Shell with about 20 radiating ribs ^^§8 



and with numerous lines of gTowth ; wings large ,^^S^ 



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 



mud flats. Fig. 905 — Pecten irradians 



_ . , , (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 irradiajis) ," by J. Risser, 

 Ann. Com. Fish., Rhode Island, 1901. 



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

 Maine, No. 6, 1906. 



