COKCHIFERA. 501 



burrowei's in mud or stone. They are often gregarious, living 

 in myriads near low- Water line, but are extracted from their 

 abodes with difiicult3\ 



Gastroch/Ena, Spongier, 1783. 



Type, G-. modiolina, PI. XXIII., Fig. 15. {Gasfer, ventra\ 

 chifiia, gape.) 



Shell regular, wedge-shaped, umbones anterior; gaping 

 widely in front, close behind; Hgament narrow, external; 

 pallial sinus deep. 



Animal with mantle closed, and thickened in front; foot 

 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 ^ 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 into a 

 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; PI. XXIIL, Fig. 15 a. 



Distribution, 10 species. West Indies, Britain, Canaries, 

 Mediterranean, Eed Sea, India, Mauritius, Pacific Islands, 

 Gallapagos, Panama ; —30 fathoms. 



Fossil, 20 species. Inf. Oolite — . United States, Europe. 



Sub-genus. Chsena, Eetz., 1788. C. mumia. PI. XXIII., 

 Fig. 16. (= Fistulana clava. Lam.) Shell elongated, con- 

 tained within a shelly tube ; posterior adductor nearly central, 

 •wdth a pedal scar in front ; siphonal inflection angular, with 

 its apex joining the pallial line. Tube round, straight, tapei- 

 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 muc"*. 

 Fossil, Inf. Oolite — . United States, Europe, Southern 

 India. 



S^iXicAVA, Bellevue. 



Etymology, saxum, stone, cavo, to excavate. S. rugcra, 

 PI. XXII., Fig. 13. 



