13fi MAZATtAN BIVALVES 



Tablet 632 contains 2 specimens, squarisli foi-m. — 633, 5 do. 

 fine flattened growth. — 634, 5 do. normal gi'owth. — 635, 3 do. 

 swollen, produced. — 636, 3 do. swollen, oval. — 637, 4 sp. shewing 

 the inside, one normal, another with the anterior teeth irregu- 

 lar, the third with the teeth nearly obsolete, the fourth do. 

 quite olisolete, appai'eutlj' from disease. 



185. Aeca eeveesa, G-ray. 



Smc. in Proc. Zool. Soc. 1833, p. ^X—MiiU. 8yn. Test. Viv. 



p. 180.— Bvc. Condi. Ic. pi. 1, f. h.—B. M. Cat. D'Orb. Moll. 



p. 81. no. 722.— C. B. Ad. Pan. Shells, p. 261, no. 421. 

 Area hemicai'dium, Koch in Phil. Ahbilcl. pi. 1, f. 1. 1843. 



This aberrant species is known at once by the truncation of 

 the anterior portion. The ligament is cut off at right angles 

 between the umbos, (which are not distant) and is solid, occu- 

 pying the posterior area. The posterior line of teeth begins 

 from the umbo ; the anterior begins from a point nearer the 

 middle, lying within the other, and is very short. There is a 

 slightly developed ridge bounding the anterior adductor, as in 

 Cuculhra. Long. \'7, lat. 2'lo, alt. 1'5. 



Hah. — Tumbez, Peru, in soft mud, 7fm., Cioning, D'Orhiy- 

 »7/.— Panama, extremely rare, C. B. Adams. — Mazatlan ; 2 

 fine specimens only were found by Mr. Archer ; L'pool Col. 



Tablet 638 contains one specunen. 



186. Aeca Pbbevifeons, Soio. 



Proc. Zool. Soc. 1833, p. 22.— Pre. Conch. Ic. pi. 1, f. 6. 



In consequence of the internal characters not being given, 

 the species cannot be determined w\{\i accuracy, but it fits the 

 ilescription as far as it goes. Epidermis as in A. multicostata, 

 very finely striated along the radiating ribs, coarsely rugose 

 between. Umbos approximate ; ligament very long and nar- 

 row. Inside white, with a subumboual stain as in A. emar- 

 ginata. Posterior hinge teeth iji a long slightly curved line : 

 anterior somewhat twisted, in a short line at a decided angle. 

 The teeth resemble A. reversa. Long. "59, lat. '4.S, all. '33. 



JTab. — Tumbez, Peru ; in soft mud, 7 fm. ; Cuming. — Mazatlan ; 

 l^p. on Murex nigritus, with A. emarginata ; L'ljool Col. 



Tablet 639 contains the specimen. 



