MOLLUSC A. 69 



of the streams of the soiithern 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. intermedins 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. lanceolatns 

 has no greater range than from Tar river, in North Carolina, to the James 

 and Eappahannoc inYirginia; 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 : 



The Unionidffi admit of being divided into three sub-families : JJnionince^ 

 Tridinince^ and EtheriincB. 



Suh-fam. 1. Unionince. 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 light from darkness, as the siphons are suddenly withdrawn when a shadow 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 thei;p 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 ENCYCLOPEDIA. VOL. II. 18 273 



