the Pholadidae into Natural Groups. 385 



** Siphonal valves without any tubular prolongation, and with a 

 longitudinal and transverse fold. Talonella. 



3. Ph. tridens. Ph. t., Sow. Thes. f. 60, 61. Talonella tridens, 



Gray, B. M. 



*** Siphonal valves with a tubular shelly prolongation. Hatasia. 



4. Ph. quadra. Ph. q., Sow. Thes. f. 62, 63. 



5. Ph. melanura. Ph. m., Sow. Ihes. f. 78, 79. Parapholas 



bisulcata, Conrad, t. 39. f. 4. 



6. Ph. tubifer. Ph. t., Sow. Thes. f. 64, 65. 



9. Talona, Gray, 1840; P. Z. S. 1848, 188. 



1. T. explanata. Ph. explanata, Spengler. Ph. candidus, Chemn. 

 f. 862. Ph. clausa, Gray, Sow. Thes. f. 74, 75. 



B. Dorsal muscle only covered with a horny skin or coriaceous epi- 

 dermis. The cavity in which the animal lives is not lined with 

 any regular shelly tube. Zirfaeana. 



10. Zirf^a, Leach MSS. ; Gray, 1840, P. Z. S. 1848. 



1. Z. crispata. Ph. c, Linn., Sow. Thes. f. 37. Ph. bifrons, 



Da Costa. Solen crispus, Gmelin. 



2. Z. constricta. Ph. c, Sow. Thes. f. 27, 28. 



3. Z. ? Darwinii. Ph. D., Sow. Thes. f. 76, 77. 



4. Z. ? julan, Adans. Seneg. t. 19. f. 1. 



5. Z. ? Vibonensis. Ph. V., Philippi, ii. t. 13. f. 5. 



11. Navea. 



Shell subglobose, closed behind ; anterior gape very large, not 

 closed up by age ; edge renexed, crenulated ; valves with a sunken 

 subcentral rib ; anterior dorsal edge reflexed and closely ad- 

 pressed to the outer surface of the valve ; dorsal muscles covered 

 with a coriaceous periostraca, and with a small transverse poste- 

 rior valve placed behind the umbones ; internal process simple, 

 elongate, arched. 



1. N. subglobosa. Shell subglobose, solid, truncated in front; 



anterior portion radiately ribbed and with a reflexed undu- 

 lated edge, hinder portion regularly concentrically grooved. 

 Hab. California, in a hole in a shell. Cab. Gray. 



2. N. tenuis. Shell ovate, subglobose, thin ; anterior portion ob- 



liquely truncated, finely and regularly concentrically stri- 

 ated, hinder portion smooth, very slightly concentrically 

 wrinkled ; subcentral rib indistinct externally, but with a 

 distinct internal rib. 



Hab. ?, in a hole in a coral. Brit. Mus. 



See also Pholas nucivora, Spengler, iv. 40. 1. 10. f. 4, 9. Very 

 Ann. $ Mag. N. Hist. Ser. 2. Vol. viii. 25 



