500 MANUAL OF THE MOLLUSCA. 
surrounded by separate areas ; siphons distinct, unequal, small, 
slightly fringed ; a minute fourth orifice close to the base of the 
branchial siphon; visceral mass large, foot small and conical ; 
mouth rather large, upper lip hood-lke; palpi tapering, few- 
plaited; gills one on each side, triangular, plaited, divided by 
an oblique line into two portions; excurrent channe!s four, two 
at the base of the gills and two below the dorsal lamine. 
(Hancock, An. Nat. Hist., 1853.) 
Distribution, 5 species. New South Wales; attached to Crass- 
atella and Trigonia, in 8 fathoms water; the fry (as indicated 
by the umbones) is free, regular, and Myadora-shaped. 
CHAMOSTREA, Roissy. 
Type, C. albida, Pl. XXIII., Fig. 14. 
Synonym, Cleidothzerus, Stutch. 
Shell inequiyalye, chama-shaped, solid, attached by the 
anterior side of the deep and strongly-keeled dextral valve ; 
umbones anterior, sub-spiral; left valve flat, with a conical 
tooth in front of the cartilage; cartilage internal, with an oblong, 
curved ossicle; muscular impressions large and rugose, the 
anterior very long and narrow; pallial line simple. 
- Animal with mantle-lobes united by their extreme edge 
between the pedal orifice and siphons; pedal opening small, 
with a minute ventral orifice behind it; siphons a little apart, 
very short, denticulated; body oval, terminating in a small, 
compressed foot; lips bilobed, palpi disunited, rather long and 
obtusely pointed; gills one on each side, large, oval, deeply 
plaited, prolonged in front between the palpi, united posteriorly; 
each gill traversed by an oblique furrow, the dorsal portion con- 
sisting of a single lamina with a free margin. (Hancock, An. 
Nat. Hist., Feb., 1853.) 
Distribution, 1 species. New South Wales. 
FAMILy X X.—GASTROCHANIDA. 
Shell equivalve, gaping; valves thin, edentulous, united by 
a ligament, sometimes cemented to a shelly tube when adult; 
adductor impressions 2, pallial line sinuated. 
Animal elongated, truncated in front, produced behind into 
two very long, united, contractile siphons, with cirrated orifices; 
mantle-margins yery thick in front, united, leaving a small 
opening for the finger-like root; gills narrow, prolonged into 
the branchial siphon. 
The shell-fish of this family, the tubicolide of Lamarck, are 
