CONCHIFERA. : 501 
burrowers in mud or stone. They are often gregarious, living 
in myriads near low-water line, but are extracted from their 
abodes with difficulty. 
GASTROCHZENA, Spengler, 1783. 
Type, G. modiolina, Pl. XXIII., Fig. 15. (Gaster, ventral, 
cheena, 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; foo4 
finger-like, grooved, sometimes byssiferous ; siphons long, sepa - 
rate only at their extremities; lips simple, palpi sickle-shaped, 
gills unequal, prolonged freely into the branchial siphon. 
G. modiolina perforates shells and limestone; its holes are 
regular, about 2 inches deep and 3 inch diameter; the external 
orifice is hour-glass shaped, and lined with a shelly layer which 
projects slightly. When burrowing in oyster-shells it often 
passes quite through into the ground below, and then completes 
its abode by cementing such loose material as it finds intoa 
flask-shaped case, having its neck fixed in the oyster-shell; in 
some fossil species the siphons were more separated, and the 
flasks have two diverging necks. ‘The siphonal orifices are 
rarely 4-lobed; Pl. XXITI., Fig. 15 a. 
Distribution, 10 species. West Indies, Britain, Canaries, 
Mediterranean, Red Sea, India, Mauritius, Pacific Islands, 
Gallapagos, Panama ; —30 fathoms. 
Fossil, 20 species. Inf. Oolite—. United States, Europe. | 
Sub-genus. Cheena, Retz., 1788. OC. mumia. Pl. XXIII., 
Fig. 16. (= Fistulana clava, Lam.) Shell elongated, con- 
tained within a shelly tube; posterior adductor nearly central, 
with a pedal scar in front; siphonal inflection angular, with 
its apex joining the pallal line. Tube round, straight, taper- 
ing upwards, transversely striated, closed at the lower end 
when complete, and furnished with a perforated diaphragm 
behind the valves. Distribution, 3 species. Madagascar, 
India, Philippines, Australia; burrowing in sand or mud, 
Fossil, Inf. Oolite—. United States, Hurope, Southern 
India. 
SAXICAVA, Bellevue. 
Etymology, saxwm, stone, cavo, to excavate. 8S. rugosa, 
Pl. XXII, Fig. 13. 2 
