PHOLADIDiE. 121 



lateral and divergent. Base of siphons protected by corneous 

 or calcareous sheaths. 



Navea, Gray, 1851. 



Distr. — 3 sp. California. N. subglobosa, G-ray (cv, 80, 81). 



Shell oval, widely gaping anteriorly, close posteriorly ; surface 

 divided by a subcentral groove ; dorsally covered by a coriaceous 

 epidermis (striated behind the interior spatulate processes), 

 under which is a small transverse posterior dorsal valve. 



Subfamily JOUANNETINjE. 

 Anterior ventral gap closed in the adult by a callous plate. 



Pholadidea, Turton, 1819. 



Syn. — Cadmusia, Leach. 



Distr. — 8 sp. W. Coast of N. America, IS'ew Zealand. P. 

 papyracea^ Sol. (cv, 82, 83). 



Shell globose-oblong, with a transverse furrow ; anterior gap 

 large, closed in the adult by a callous plate ; two minute acces- 

 sor}^ 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 (in adults). 



HAT ASIA, Gray, 1851. Siphonal cups or valves with a tubular 

 shelly prolongation. P. melanura, Sowb. 



TALONELLA, Gray, 1851. Siphonal valves without any tubular 

 prolongation, and with a longitudinal and transverse fold. P. 

 tridens^ Gray. 



NETASTOMELLA, Carp. Based upon Ph. Darwinii, Sowb., 1865. 

 The valves are posteriorly prolonged into a flattened calcareous 

 cup. Differs from Jouannetia in having both valves equal, and 

 from Pholadidea by the calcareous nature of the cup at the pos- 

 terior end of the shell. 



Jouannetia, Desmoulins, 1828. 



Syn. — Triumphalia, Sowb., 1849. 



Distr. — 2 sp. Philippines. 



Shell very short, subglobose, with two impressed radiating 

 grooves ; 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. 



PHOLADOPSis, Conrad, 1849. Yalves with a single subcentral 

 radiating groove. J. pectinata, Conr. (civ, 63). California. 



Parapholas, Conrad, 1848. 

 Distr. — 2 sp. California, Australia. Fossil; Cretaceous. P. 

 Californica, Conr. (civ, 64). 

 Shell oval-oblong; anterior gap closed by a thin, swollen, glo- 



