476 MOLLUSCA. 
P. Carpenter, Rep. Moll. N.W. Amer. p. 188 (1856) °; vy. Mart. in Martini & Chemnitz, 
Syst. Conch.-Cab. ed. 2, Neritina, pp. 116, 280, t. 18. figg. 3, A”, 
Hab. 1 Panama? 5, 
I have examined the shell and operculum of a specimen given by Cuming to 
Consul Gruner in Bremen, and now in the Berlin Museum, and feel much inclined 
to adopt Récluz’s + view that it is identical with V. variegata, Less., from the Malayan 
Archipelago. The locality “Panama” is not given in the earlier records! *, and the 
species is not included in C. B. Adams's list of Panama shells. 
Neritina michaudi. 
Neritina michaudii (Récluz), Sowerby, Thes. Conch. ii. p. 529, t. 112. figg. 108, 109, t. 115. 
figg. 217, 2181; Reeve, Conch. Icon. ix., Neritina, t. 25. fig. 109°; P. Carpenter, Rep. 
Moll. N.W. Amer. pp. 189, 291, 322 (1856) *. 
A species of British India, incorrectly recorded from Panama by Sowerby and Reeve 
(see my Monograph of this genus, p. 191). 
Neritina mexicana. 
Neritina mexicana (Parreyss), in Paetel’s Cat. Conchylien-Sammlung, ed. 4, p. 524 (1888) *. 
Hab. Mexico }. 
The specimen in Paetel’s collection is identical with the European WV. danubialis, Meg. 
BIVALVIA. 
Shells composed of two corresponding halves (valves), a right and a left. 
Also known under the names Conchifera (Lamarck), Lamellibranchia (Cuvier), 
Dithyra (Turton), and Pelecypoda (Goldfuss). 
As there is still much difference of opinion among conchologists regarding the larger 
subdivisions of the Bivalvia, we prefer to name only the families; very few of them are 
represented in freshwater. 
Fam. DREISSENIDZ. 
Characters the same as those of the only genus. 
DREISSENA. 
Dreissena, Van Beneden, Ann. Sciences Nat. (2) iii. p. 193 (with description of the living animal) 
(January 1835). 
Tichogonia, Rossmassler, Icon. Land- und Sisswasser Mollusken, i. 1, p. 112 (April 1835). 
Dreissensia, Fischer & Crosse, Miss. Scient. Mex., Moll. ii. p. 497. 
Form of the shell unequilaterally triangular, pointed before, rounded behind, as in 
