LUTRARIA. 



The LutrariaB are generally thin^ equivalve^ inequi- 

 lateral, transversely ovate or oblong shells, the posterior 

 side for the most part the longer, but always gaping 

 much more than the anterior side, which nevertheless 

 gapes a little. Hinge of one valve with two teeth, of 

 which one is sometimes compound, the other valve with 

 three teeth, of which the center one is sometimes com- 

 pound, and the posterior one is slender and compressed. 

 Ligament internal, fixed to a deltoid, oblique, internally 

 prominent pit placed next to the teeth in each valve. 

 Muscular impressions two, lateral, distant : muscular im- 

 pression of the mantle with a large sinus. 



Of Lutraria the recent species are not numerous; 

 several of those admitted to the Genus by Lamarck, are 

 found on our coasts, particularly the L. Solenides, (which 

 we believe to be Mactra hians of British writers) the L. 

 elliptica, (Mactra Lutraria, Linn.) and L. compressa, 

 (Ligula compressa, Mont.) which latter we think ap- 

 proaches more nearly to the Amphidesmata than to the 

 LfUtrarice. A few species are rather thick, but by far the 

 greater number are extremely thin, delicate and fragile 

 shells. Of the thicker species the L. Solenoides, and of 

 the thinner the X. plicatella may be cited as characteristic 

 examples. 



There are very few fossil species, perhaps none at 

 all, for most of those hitherto called Lutrarige, are proved 

 to belong to other genera, and others are uncertain; 

 while Lamarck's L. crassideus should by him have been 

 arranged with his Coi^ulce^ though we are of opinion, 

 that it should be united to some other shells that are 

 found in the rivers of vv^arm climates, and with them form 

 a distinct Genus. 



We have represented 



Fig. 1. The insides of both valves of Lutraria solenoides. 



2. A shell commonly called the Duck's Bill Mactra, but which we cannot 

 refer with certainty to any published description or figure : we should consider 

 it to be Lamarck's Lutraria papyracea, if it agreed as well with the figure cited 

 in End, Meth. t. 257, f. 2, as it doeti with his description. 



