26 
double ; outer more or less expanded and reflexed, covering (per- 
haps all) the shell; inner covering the gape of the shell. Gills 
two pair, dependent, united together behind the foot. Lips elon- 
gate. Shell oblong, equivalve, gaping behind. Hinge toothless. 
Cartilage internal, in a triangular pit. 
1. Galeomma. 
1. G. Turtoni, t. 334. f. 7, 9, t. 34 7. f. 4. 
2. G. tongensis, t. 334. f. 5. 
VI. Foot very small , rudimentary, byssiferous. Hinder adductor 
muscle large, placed forward in the centre of the lower edge 
of the shell. Pedal opening small in front near the umbo. 
Anal opening apparently behind and above the hinder adduc- 
tor muscle. 
Fam. 24. Tridacnidce. 
Foot small. Anterior adductor muscle very small. Mantle 
double-edged; inner edge expanded. Gills small, thick, pinnate, 
united behind the foot. 
1. Tridacna. 
1. T. mutica, t. 335. f. 2, t. 336. f. 2. 
2. T. , t. 336. f. 1. 
3. T. crocea, t. 335. f. 3 (fig. 9). 
Fig. 9. — Tridacna crocea. 
p, pedal orifice, b, byssus. f, foot, y, gills, a, posterior adductor 
muscle. I , pallial muscle, s, siphons — i, branchial ; e, anal. 
2. Hippopus. 
1. H. maculatus, t. 335. f. 1. 
