BNO DON. 
Prate L 
Genus ANODON, Bruquiére. 
Testa fluviatilis, bivalvis, bimusculosa, transverse oblonga, 
plerumque plus minusve ovata, intus margaritacea, 
margine cardinali edentuld, extus epidermide corned 
induta ; ligamento externo. 
Shell fluviatile, bivalve, bimuscular, transversely oblong, 
generally more or less ovate, pearly within, with 
toothless cardinal margin, covered with a horny 
epidermis without, ligament external. 
Although the great rivers of the North American 
Continent may be regarded as the favoured haunts of 
the Nayades, as they produce the greatest number of 
species in the greatest abundance and fullest develop- 
ment, yet they possess nothing like a monopoly of the 
family. In every part of the world, wherever rivers or 
large ponds or inland lakes exist and can be explored, 
there are to be found numerous members of the family, 
the Anodcns with toothless hinges side by side with the 
more ponderous divisions of the tribe, the Unios, whose 
generally thickened shells may be supposed to require 
more strength and complexity in their cardinal arrange- 
ments. Thus in our own rivers we have one or two 
large species of Anodon to correspond with our two or 
three Unios, and so on through all the European States. 
Australia and India supply their quota of both divi- 
sions, and perhaps there is no general peculiarity dis- 
tinguishing the Nayades of those localities from the 
European and Nerth American types. There is, how- 
ever, in Central America a rather peculiar type of nu- 
merous species, which some naturalists have considered 
generic, and have distinguished under the name of 
Leila. They are rather solid shells, with a triangular 
‘notch in the pearly lining of the posterior part of the 
hinge, and a sinuous hiatus in the front ventral margin. 
The Brazilian species, Anodon scriptus and Anodon 
hians, represented in Plate IV., show these charac- 
teristics in a very pronounced manner. The variation 
of form to which the species are liable, the differences 
which are presented in various stages of development, 
and the expanding or stunting influences of local cir- 
cumstances, render the determination of species a work 
of the greatest difficulty, or it might be said, absolute 
impossibility. Probably many so-called species de- 
scribed by Lea and others, possibly some of the few to 
which new names are herein attached, may be but 
varietal forms of previously known species. It would 
| be impossible, without having the specimens of all the 
| great collections before us at once, to form a perfectly 
| consistent opinion in every case. 


The most we can do, 
is what I have endeavoured to do here, namely, to find 
or adopt designations for the more palpably distinct 
forms coming under our cognizance. 

Species 1. (Mus. Sowerby.) 
ANODON GRANDIS. An. testé subtrigond, altd, magna, 
inflata, tenui concentrice leviter undulata, fumeo- 
Suscd, eradiata, ad umbones et intus fulvida : latere 
antico producto, subrotundo ; medio injflato, margine 
ventrali convexo, umbonibus elevatis, magnis, promi- 
nentibus, subcentralibus; latere postico productitsculo, 
obliqué angulato, infra ad terminum acuminato, mar- 
gine dorsalielevato,recto, margine laterali subconcavo, 
valdé declivi. 
LarGE Anopon. Shell trigonal, elevated, large, 
inflated, thin, concentrically lightly undulated, 
smoky brown, without rays, fulvous at the umboes 
THE 
and within; anterior side produced, rather rounded; 
middle inflated, ventral margin convex, umboes 
elevated, large, prominent, subcentral; posterior 
side a little more produced, obliquely angular, 
acuminated at the end below, dorsal margin 
elevated, straight, lateral margin a little concave; 
much sloped. 
Say. Jay’s Catalogue of Shells, p. 25. 
Hab. Fox’s River, U.S. 
There are specimens of this shell in the British 
Museum marked Anodon anatina, Lamarck, but the 
expression ‘“ Natibus retusis” in the description is de- 
cisive against Lamarck’s name being applied to this 
species. 
June, 1870. 
