GASTROCH ANID. 119 
and slender; gills 2 on each side, elongated, narrow (floating 
freely in the branchial siphon 7). 
Some specimens of the recent C. aperta have 3 frills to their 
tubes ; C. bacillaris has twice that humber occasionally. They 
are formed by the siphonal orifices when the animal continues 
elongating, after having fixed its valve and ceased to burrow ; 
or perhaps, in some instances, when it is compelled to lengthen 
its tubes upwards by the accumulation of sediment. Brocchi 
mentions that on breaking the tube of the fossil C. echinata, he 
sometimes found the shell of a Saxicava or Petricola beside the 
loose valve of the Clavagella, into whose tube they must have 
entered after its death. C. elongata is found in coral; C. Aus- 
tralis lives at low tide, and spurts out water when alarmed. 
CLAVAGELLA (restricted). Only known in a fossil state, having 
the lower end of the tube surrounded by hollow spinous pro- 
cesses. 
STIRPULINA, Stoliczka. Valves ovate, subequal, similar to those 
of Clavagella, but tubuli formed only at the front part of the 
tube which has a distinct fissure; tube long. Clavagella coronata 
or bacillaris of Desh. A fossil group only. 
BRYOPA, Gray, 1840. (Recent.) Lower end of tube simple ; 
siphonal end frilled. C. aperta, Sowb. (civ, 45). Mediterranean 
Sea. 
pacosta, Gray, 1840. (Recent.) Lower and siphonal ends of 
tube both simple. C. Australis, Sowb. 
SuBFAMILY GAST'ROCHA NINA. 
Shell with both valves free from the tube. 
GAsTROcCHANA, Spengler, 1780. 
Syn.—Chena, Retz., 1788. Fistulana, Brug., 1789. 
Distr.—3 sp. Madagascar, India, Philippines, Australia ; 
burrowing in sand or mud. Fossil. Cretaceous; United States, 
Europe, Southern India. G. mumia, Spengler (cv, 67, 68). 
Philippines. 
Shell elongated, narrow, contained within a shelly tube; pos- 
terior adductor nearly central, with a pedal scar in front; siphonal 
inflection angular, with its apex joining the pallial line. Tube 
round, straight, tapering upwards, transversely striated, closed 
at the lower end when complete, and furnished with a perforated 
diaphragm behind the valves. 
Animal elongated, rounded, cephalic extremity swollen; 
siphons united, long. 
RoceriariA, Bellevue, 1802. 
Syn.—Gastrochena, Cuv., 1817. Roxellaria, Agassiz. 
Distr.—10sp. West Indies, Britain, Canaries, Mediterranean, 
