MAZATLAN BIVALVES 13 



Hob. Panama, in limestone rocks at low water, Cuming. 



Mazatlan ; not uncommon ; L'pool Col. 



Tablet 38 contains 3 normal specimens. 39, 3 do. distorted. 

 40, 2 do. shewing inside, and plates. 



GENUS MAETESIA, Leach. 



Differing from Pholadidea in the large development of the 

 accessory plates ; from Parapholas in the cups not being per- 

 sistent. 



19. MAETESIA INTEECALATA, n. *-. 



M. t. parvd, subglobosd, in duas paries divisd ; parte 

 anterior e tenuissime concentrice striatd, radiis longitudinalibus 

 subobsoletis vix undatd ; in juniore maxime Jdante, margin? 

 solido ; in adult A secretione semi-corned clous d : parte posticd 

 subl&vi, epidermide copiose indutd, margine rotundato ; um- 

 bonibus testa reflexd adhcerente ccelatis ; clypeo pyr\ iforme , parvo, 

 solido, inter secretiones valvarum inter cal ante ; 

 partibus ventrali et dorsali laminis semi-corneis, brevibus, a 

 calyce repulsis ; calyce piano, brevi, simplici, extanle. 



The species is named from the remarkable way in which the 

 umbonal shield pushes itself in anteriorly between the project- 

 ing portions of the closed valves ; and in which the cup, which 

 pouts out from the otherwise rounded extremity, pushes itself 

 in between the anterior and posterior plates, cleaving them and 

 thrusting them back. Mr. Haiiley was fortunate enough to 

 find two specimens burrowing in Spondylus, of which the larger 

 has not yet closed the anterior portion, but the smaller is adult. 

 The .shield does not fold round the dorsal plate. The whole 

 dorsal and posterior part has a thickened raised margin, pro- 

 bably epidermal. The largest (adolescent) specimen measures 

 long. '34, lat. '35, alt. *33. The cup in. the smaller specimen 

 measures '06. 

 Hab. Mazatlan ; in Spondylus Lamarckii, extremely rare ; 



Havre Col. 



Tablet 41 contains various magnified sketches of the two 

 specimens in Mr. Hanley's collection. 



20. . 



A curious little fragment, unfortunately too imperfect for 

 identification, which may belong to a Pholad, but is certainly 

 distinct from any of the foregoing. Shell with a strong, irre- 

 Aug. 1855. c 



