MOLLUSCA. 69 
of the streams of the southern shore of Lake Superior, and thus belongs to 
the basin of the St. Lawrence: it is found in Maine, and probably in every 
river as far south as the Savannah. Species are found in east Tennessee, 
as U. intermedius and subtentus, which are not found in Kentucky or the 
States on the south; and Louisiana has species not found beyond its limits. 
Unio plicatus and siliquoideus (the latter found in Lake Champlain, and the 
former above Pittsburgh, and in Grand river, Michigan) are found as far 
towards the southwest as San Antonio in southern Texas. U. lanceolatus 
has no greater range than from Tar river, in North Carolina, to the James 
and Rappahannoc in Virginia; and U. collinus, subplanus, and constrictus, 
seem not to extend beyond James river. 
The following table exhibits the distribution of some of the species of the 
Atlantic rivers, from the Connecticut to the James. Asterisks under the name 
of a river denote the presence of a species in it, and dots indicate where it 
has not been found. The three first on the list extend into Maine: 
Cénnecticut, Hudson, Delaware, Susquehanna, Potomac, James. 
U.complanatus, , x » XXX % % % Hx xx X x & % 
radiatus, % % % HHH HX xxx x % 
ochraceus, x x x xx % eK ai xX Hx 
cariosus, %*% xX eX LHX x ** x*% 
heterodon, xxx saa cic a ee 
nasutus, ee % %% xX * ole HRX HEH 
viridis, at: HHH xe % HHH HEX HHH 
The Unionide admit of being divided into three sub-families : Unionine, 
Tridinine, and Htherune. 
Sub-fam.1. Unionine. The labial palpi are four: the foot is large and 
linguiform ; the mantle is not united, and the posterior siphons are not tubular, 
being formed by the mere contact of its posterior margin on each side, but 
leaving two openings. The extremity scarcely extends beyond the shell; it 
is papillate, and provided with eyes which have the power of distinguishing 
light from darkness, as the siphons are suddenly withdrawn when a shadow 
is cast upon them. Some genera of this sub-family present no distinctive 
characters by which an Unio or an Anodonta, &c., can be distinguished 
without the shell, and on this account some authors insist that a character 
is worthless in the shell if unaccompanied by some distinction of the soft 
parts; and forgetting that the shell is part of the animal as the bill is part 
of a bird, they insist upon having two characters instead of one.. 
In the genus Unio there are two cardinal teeth in each valve anteriorly, 
and a lamellar tooth posteriorly in the right valve, fitting between two in 
the left one. 
Anodonta has the hinge margin without teeth, and the shell is usually 
thin in texture. 
Alasmodonta has cardinal teeth, but no lamellar teeth. Say founded this 
genus in 1818, and it was named Margaritana by Schumacher, in a work, 
the title-page of which bears the date of 1817. “The priority of this date 
ICONOGRAPHIC ENCYCLOP £DIA.—VOL, II. 18 273 
