BIVALVES AND CUTTLES. 



287 



KEY FOR IDENTIFICATION OF COMMON BIVALVES. 

 BIVALVES, or LAMELLIBRANCHS. 



(1) Filibranchs, with filamentous or thread-like gills. 

 Shell of irregular ^ 



shape, lower valve V Surface scaly, without ribs Anomia ephippium. 

 with aperture . J 



'Shell wedge - shaped, % 



beaks terminal, colour I Mytilus edulis. 

 blue . . . J 

 Shell oblong, swollen in^ 



front, beaks anterior, \Modiola modiolus. 

 colour dark purple . J 

 Shell short and tumid, ^ 



CS$! <" """ 



yellow . . . J 



(2) Pseudo - lamellibranchs, gill -filaments only slightly attached 



Shell equivalve, oval 

 or oblong, beaks 

 incurved, hinge" 5 

 without teeth 



together. 



Shell suborbicular, inequi- 

 valve, marked with ribs, 

 beaks with distinct ears, 

 shell not gaping, brightly 

 coloured 



Pecten 



Lima 



Ribs 20, surface with minute 



scales P. opercularis. 

 Ribs 14 to 16, surface with 

 radiating striae P. maxi- 

 mus. 



Ribs 40 to 60, prickly on 

 upper valve only P. 

 > pusio. 



Shell like the above, " 

 gaping, colour white, 

 valves equal 

 Shell irregular, ineq ui valve, ^ 



upper valve flat and lower \ Ostrea 

 concave, teeth absent . J 

 (3) Eulamellibranchs, gills plate-like, the filaments firmly attached 

 together. 



(a) Shell closed. 

 Shell oval, with distinct 1 

 epidermis and external I 

 ligament, no pallial f W rina 

 sinus . . . . J 



" Shell solid and opaque, 



triangular M. solida. 

 Similar, but smaller, more 

 convex, and with more 

 prominent beaks M. 

 subtruncata. 



/Shell oblique, gaping widely 

 ' \ at both sides L. Mans. 



{Shell round in young, and 

 later becoming irregular 

 0. edulis. 



f Shell obliquely triangular, 

 -j swollen towards beaks 

 v C. islandica. 



Shell triangularly oval, 

 slightly striated, with 

 deep sinus, cartilage 

 internal 



Maetra 



Shell thin, glossy, with 

 brownish rays M. stul- 

 torum. 



