CONCHIFERA. 329 



PHOLADIDEA, Turton, 1819. 



Type, P. papyracea, PI. XXIII. fig. 20. 



Shell globose-oblong, with a transverse furrow; ; anterior gape large, 

 closed in the adult by a callous plate ; 2 minute accessory valves in front of 

 the beaks. 



Animal with a fringed disk at the end of the combined siphons, and a 

 horny cup at their base. 



Distr. 6 sp. Brit. N. Zealand, Ecuador. Low-tides 10 fms. 



Sub-genera. Martesia (Leach) Bl. 1825. M. striata, PI. XXIII. fig. 21 

 Valves lengthened behind, when full grown, by a plain border ; umbonal 

 valves 1 or 2 ; dorsal and ventral margins often with narrow accessory valves. 

 10 sp. W. Indies, Africa, India. M. striata burrows in hard timber. M. 

 terediniformis was found in cakes of floating wax on the coast of Cuba. 

 (G-. B. Sby.) M. australis in (fossil ?) resin, on the coast of Australia. M. 

 rivicola in timber 12 miles from the sea, in Borneo. M. scutata, Eocene, 

 Paris, lines its burrow with shell. 



Jouannetia (semicaudata) Desm. (Pholadopsis, Conrad; Triomphalia, 

 Sby.) Shell very short, sub-globose ; right valve longest behind : anterior 

 opening closed by a callous plate developed from the left valve overlapping 

 the margin of the right valve, and fixed to the single unsymmetrical umbonal 

 plate. Distr. 3 sp. Philippines, W. America. Fossil, Miocene . Prance. 



Parapholas, Conrad, P. bisulcata, PL XXIII. fig. 22. Valves with 2 

 radiating furrows. Distr. 4, sp. California, Panama, Torres Strts. 



XYLOPHAGA, Turton. 



Etym. Xulon, wood, phago, to eat. 



Types, X. dorsalis, PL XXIII. fig. 23 ; X. globosa, Sby. Valparaiso. 



Shell globular, with a transverse furrow ; gaping in front, closed behind ; 

 pedal processes short and curved ; anterior margins reflected, covered by 2 

 small accessory valves ; burrow oval, lined with shell. 



Animal included within the valves, except the slender contractile siphons, 

 which are furnished with pectinated ridges, and divided at the end ; foot 

 thick, very extensile. 



Distr. 2 sp. Norway, Brit. S. America. Bores an inch deep, and across 

 the grain, in floating wood, and timbers which are always covered by the sea. 



TEREDO (Pliny) Adanson. 



Type, T. Norvegica, PL XXIII. figs. 26, 27. Syn. Septaria, Lam. 



Shell globular, open in front and behind, lodged at the inner extremity of 

 a burrow partly or entirely lined with shell ; valves 3 lobed, concentrically 

 striated, and with one transverse furrow ; hinge-margins reflected in front 

 marked by the anterior muscular impressions ; umbonal cavity with a long 

 curved muscular process. 



