100 On the Animals of certain Genera of Bivalve Shells. 



siphon with six longitudinal bands ; anal siphon smaller, with 

 eight bands ; siphonal muscle moderate, orbicular ; siphonal 

 chamber small. Foot large, compressed, liuguitbrm ; adductors 



a, a, adductor musfles ; p, p, p, pedal muscles ; the arrows indicate the 



inhalent and exhalent siphons (much contracted), 

 rounded ; pedal muscles close to adductors, large, oblong. Palpi 

 broad at tlie base, tapering suddenly, very delicate, their front 

 border plain. Gills two on each side, recumbent, rather small, 

 unequal, plaited, united behind; inner gill largest, prolonged 

 between the palpi, its inner surface smooth ; outer gill much 

 shorter, attenuated in front, with a free, plaited dorsal border. 



Tridacna crocea, liam. 



Mantle margins {m) double, plain, united by a curtain pierced 

 with three orifices. Siplional orifice on the ventral side, sur- 

 rounded by a prominent and thickened border (s) ; branchial 



orifice (i) moderate, simple ; anal (e) remote, behind the centre, 

 with a tubular valve. Byssal orifice {p) large, close to the 

 umbo, occupying nearly the whole anterior side. Byssus {h) veiy 

 large. Foot (/) small, finger-like, grooved ; pedal muscles 

 thick, attached behind the great adductor. Adductor (posterior) 

 round, large, central («). Pallial muscle (/) thick. Gills {g) 



