MAZATLAN BIVALVES 117 



Family UNIONIDJi:. 



Genus AT^ODONTA, Cuv. 

 Anodonta, Cuv. Tabl. EUm. 1798. — Anodon, Oken, 1815. 



166. Anodonta ciconia, Gould. 



Anodon ciconia, Gould Proc. Bost. Soc. IVaf. Hist. vol. iv. 



p. 92, Ts^ov. 1851 -.—Ilex. ^" Cal. Shells, p. 29. 

 Anodon siuuata, Swains, (as of Lam. uon A. sinuosa, An. s. 



Vert. vol. yi., p. 569, no. 14.) Exot. Conch, p. 29, pi. 16, edit. 



Manl. 



Distinf^uisked from A. anserina, (Brazil,) according to Gould, 

 by being tliicter, more tumid on tlie posterior half, epidermis 

 and nacre differently coloured. The nearest N. American 

 species is A. implicata. It varies in shajje, but may generally 

 be known by its somewhat solid growth, ventral gape, and 

 salmon colour within. In the young shell, the tint is silvery, 

 light or flesh colour. Long. 2 '32, lat. 4 "24., alt. 1"46. 



Sah. — ? Mexico, Lieut. Green. — Mazatlan ; not uncommon ; 

 L'pool ^ Havre Coll. 



Tablet 523 contains 3 sp. elongated form. — 524, 2 sp. inter- 

 mediate. — 525, 2 sp. produced ventrally, epidermis glossy with 

 faint radiating lines of colour.— 526, 1 sp. with concentric 

 striae near the umbos.— 527, 2 sp. distorted. 



Family MYTILIDiE. 



Dr. Dunker is at the present time engaged on a monograph 

 of this family, of which the first part onh' (Monograph of the 

 genera Septifer and Dreisscna) is as yet published. He has 

 however most kindly identified the Mazatlan species with 

 his own, and given me much valuable information concerning 

 them. The young shells not only of different species, but 

 even of different genera, very closely approximate each other. 



The measurements in this family are taken as follows ; long. 

 from umbo to posterior extremity ; lat. from dorsal extremity 

 of ligament straight across to ventral margin : alt. thickness 

 of closed valves. 



