COKCHIFERA. 335 



Distr. 3 sp. New South Wales ; attached to Crassatella and Trigonia, 

 in 8 fm. water; the fry (as indicated by the umbones) is free, regular, and 

 Myadora- shaped. 



Chamostrea, Roissy. 



Ttjpe, C. albida, PI. XXIIT. fig. 14. Syv. Cleidothaeriis, Stutch. 



Shell inequivalve, chama-shaped, solid, attached by the anterior side of 

 the deep and strongly-keeled destral 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 pedaJ 

 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 ob- 

 tusely pointed ; gills one on each side, large, oval, deeply plaited, prolonged 

 in fi'ont betvpeen the palpi, united posteriorly ; each gill traversed by an 

 oblique furrow, the dorsal portion consisting of a single lamina with a free 

 margin. (Hancock, An. Nat. Hist. Feb. 1853.) 



Distr. ] sp. New South Wales. 



FAMILY XX. Gastroch^nid.e. 



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 very 

 thick in front, united, leaving a small opening for the finger-like foot ; gills 

 naiTow, prolonged into the branchial siphon. 



The shell-fish of this family, the tuhicolidoB of Lamarck, are burrowersin 

 mud or stone. They are often gregarious, living in myriads near low-water 

 line, but are extracted from their abodes with difiiculty. 



Gastroch^ena, Spengler, 17C3. 



Type, G. modiolina, PI. XXIII. fig. 15. {Gaster, ventral, cJiana, gape.) 



Shell regular, wedge-shaped, umbones anterior ; gaping widely in front, 

 close behind ; ligament narrow, external ; pallial sinus deep. 



Animal with mantle closed, and thickened in front ; foot finger-like, 

 grooved, sometimes byssiferous , siphons long, separate only at their extre- 

 mities ; lips simple, palpi sickle-shaped, gills unequal, prolonged freely into 

 the branchial siphon. 



G. modiolina perforates shells and limestone ; its holes are regular, about 



