MALACOZOA. TROPIOPODA. 1AMELLIBRANCHIATA. 203- 



OF THE ABERDEENSHIRE SPECIES. 

 ORDER I. TROPIOPODA LAMELLIBRANCHIATA. 



Kespiratory organs of two unequal pairs of very thin 

 expanded branchiae, on the sides of the body, within the 

 mantle. 



Lamella, a thin plate ; branchia, gills. Blainville. 



MONOMYARIA. A Single Adductor Muscle. 

 FAMILY I. PECTININA. 



Body roundish, compressed, with the lobes of the 

 mantle disunited beneath, their margin thickened and 

 fringed with filaments ; the foot very small. Shell in- 

 equivalve, auriculate, more or less radiatingly costate or 

 striate, the hinge toothless, with a central depression for 

 the ligament ; the muscular impression very large, sub- 

 central. Named from the genus Pecten. 



GENUS 1. PECTEN. Shell free, regular, inequivalve, 

 roundish, compressed, divergently costate ; umbones 

 very small, pointed ; ligament internal, trigonal. Pecten, 

 a comb. Lister. 



1. Pecten mdximus. Shell nearly orbicular, inequi- 

 valve, with sixteen convex ribs, which, with their nearly 

 equal convex interstices, are longitudinally striate ; the 

 upper valve flat. Named from being the largest known. 



2. Pecten opercularis. Shell nearly orbicular, inequi- 

 valve, with twenty-two convex subcarinate ribs, which, 

 with their concave interstices, are longitudinally striate, 

 and transversely lamelloso-striate ; the upper ^alve con- 

 vex. Opercularis, resembling a lid. 



3. Pecten vdrius. Shell roundish, somewhat oval, 

 nearly equivalve, with about thirty-two rounded, some- 

 what compressed, irregularly echinato-laminate ribs. 

 Varius, of different colours. 



4. Pecten Isabella. Shell roundish-oval, nearly equi- 

 valve, little convex, with twenty-four slender, compressed, 



