GASTROCHiENlD^. 119 



and slender; gills 2 on each side, elongated, narrow (floating 

 freely in the branchial siphon ?}. 



Some specimens of the recent G. aperta have 3 frills to their 

 tubes ; C. bacillaris has twice that number occasionall3^ 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 b}'' the accumulation of sediment. Brocchi 

 mentions that on breaking the tube of the fossil G. ecliiuata^ he 

 sometimes found the shell of a Saxicava or Petricola beside the 

 loose valve of the Clavagella, into whose tube the}^ must have 

 entered after its death. G. elorigata is found in coral ; G. Auh- 

 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. Yalves 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. Glavagella coronata 

 or bacillaris of Desh. A fossil group only. 



BRYOPA, Gray, 1840. (Recent.) Lower end of tube simple ; 

 siphonal end frilled. G. aperta^ Sowb. (civ, 45). Mediterranean 

 Sea. 



DACOSTA, Gray, 1840. (Recent.) Lower and -siphonal ends of 

 tube both simple. G. Australis^ Sowb. 



Subfamily GA S TR GEMNINjE. 

 Shell with both valves free from the tube. 



Gastroch^na, Spengler, 1180. 



Syn. — Chsena, Retz., 1T88. Fistulana, Brug., 1*789. 



Diatr. — 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. 



Rocellaria, Bellevue, 1802. 

 Syn. — Gastrochsena, Cuv., 1811. Roxellaria, Agassiz. 

 Distr. — 10 sp. West Indies, Britain, Canaries, Mediterranean, 



