230 MALACOZOA. TROP10PODA. LAMELLIBHANCHIATA. 



but his figure is very incorrect. It seems to be nearly allied 

 to Pecten and Lima, and to have a single muscle only, although 

 the impression is not defined. 



Mytilus decussatus. Mont. Test. Brit. Suppl. 69. Mytilus de- 

 cussatus. Laskey, Wern. Mem. i. 394. PI. 8. f. 17. Crenella 

 elliptica. Brown, Illustr. PI. 3J. f. 12, 13, 14. Mytilus decussatus. 

 Flem. Brit. Anim. 411. 



GENUS 4. ANOMIA. SCALE-OYSTER. 



Animal roundish, very much compressed. The lobes 

 of the mantle very thin, their margins furnished inter- 

 nally with a row of tentacular filaments. Foot very 

 small. Mouth with prominent lips, aud on each side 

 two pairs of triangular palpi. Branchiae filamentous. 

 Adductor muscle divided into three portions, of which 

 the largest passes through an opening in the flat valve, 

 and attaches the animal to some solid body by means of 

 a hard lamina. 



Shell roundish, irregular, inequivalve, delicate, fragile ; 

 the lower valve flat, or having the curves of the surface 

 to which it is applied, with a roundish aperture or notch 

 near the hinge for the attachment of the animal to some 

 hard substance. 



The species live affixed to stones, crabs, shells, fuci, 

 and other substances. 



1. Anomia Epldpplum. Saddle Scale-Oyster. 



Shell roundish, but variable, thin, somewhat translucent, 

 white; the upper valve little convex, irregularly undulated, 

 squamoso-lamellate, with the beak small ; lower valve very 

 thin, uneven, concentrically striated, with the aperture oval; 

 opercular plate thickish, concentrically striated. 



It varies greatly in form, thickness, convexity, and mark- 

 ings, as well as in colour, being frequently tinged with green 

 on its inner surface. " Happening to be attached to Pectens," 

 says M. Deshayes, " the individuals of this species, as well as 

 of others of the same genus, are impressed upon the ribs, of 

 which their shell takes the form. This is so true, that it is not 

 rare to meet with individuals of which the ribs run transversely, 

 while in others they are oblique, and others have the ribs broad 

 toward their summit, narrow toward their margins, because 



