ZIRPHiEA. 327 



Shell globose, gaping widely in front, closed behind; 

 valves divided by a transverse furrow ; accessory valves 

 two, half-ovate, small, diverging. Umbonal process none, 

 but the anterior margins of the valves reflexed ; pedal pro- 

 cesses short and curved. 



Ex. X. dorsalis, Turton, pi. 89, fig. 4. Shell, X. dor- 

 salis, fig. 4, a, 4, b, 4, c. 



The Xylopliaga is found boring in floating wood, usually 

 forming burrows across the grain about an inch deep, which 

 are oval and lined with shell ; the species have been found 

 in Norway, Britain, and South America. 



Species of Xylopliaga. 

 dorsalis, Tart. globosa, Sow. 



Genus ZIRPH^A, Leach. 



Shell ovate ; umbonal muscle only covered with a horny 

 or coriaceous epidermis ; no dorsal valves ; hinge-plate not 

 reflexed over the beak; anterior gape always open, not 

 closed in the adult by a callous plate. 



Syn. Zirfeea, Gray. 



Ex. Z. crispata, Linnaeus, pi. 89, fig. 5, 5, a. 



In this genus there are no umbonal, shelly valves, the 

 beaks being protected only by a membrane. 



Species of Zirphaa. 



Beauiana, Recluz. crispata, Linn. 



constricta, Sow. julan, Adams. 



