FRESH WATER AND LAND SHELLS. 23 



of tlie cardinal tooth; pallcal cicatrices impressed; cavity of the shell very shallow; cavity 

 of the beaks rather deep and angular; nacre silvery white. 



Remarks. — The curious and beautiful interrupted rays which cover the whole disk of 

 this species, bring it into the group of which the U. irroratus, (Nobis,) was the first 

 described, and may be considered the type. There are now four known, all of which, while 

 easily distinguished, have very much the same general characteristics, — irroratus, dromas, 

 capcralus and Lamarckianus. The five specimens before me are of diflerent sizes. The 

 largest is the most perfect one, and is that which is figured. It is about the size of a 

 young dromas, when about to finish its two humps. It differs from all the other three 

 species, in having an angular ridge from the beaks to the posterior basal margin. The 

 beaks are remarkably compressed and pointed, like securis, (Nobis.) The nodules arc 

 little more than rugosities, disposed to run into small folds. Both this and caperalus 

 might be said scarcely to belong to the nodulous division of the genus, but they are cer- 

 tainly not devoid of nodules, though they are small and irregular. The lines of growth 

 are very different from caperalus. In the latter they are very close. In outline, the 

 Lumarckiamis is nearly the same with intermedins. Con., from Tennessee. It cannot, 

 however, be confounded with that species, as it has not the furrow which that shell has 

 on the posterior slope; nor has it the well expressed verrucosc character of it. It differs 

 also in the rays, which in intermedias are arrow-head shaped. Indeed the intcrmcdius 

 belongs to another group, of which metanever, Raf., may be considered the type. 



I dedicate this beautiful species to the memory of the great naturalist Lamarck. 



Uniohebes. pi. XVIII. Fig. 21. 



Testa Ixvi, ol)ton2;i't, subcnnipressi'i, ad latere plamdatd, iniequUaternli, postice tnmcalu; vatvulis stilicrassis; 

 nalibus subprominentibus, ad apices undutatis; epidermide striata tenebroso-fuscd, eradiatii ; denlibus cardi- 

 nutibus subcrassis, compressis, obtiquis, acuminatis ; lateralibus tongis ctirvisqtie ; margaritd alba. 



Shell smooth, oblong, rather compressed, flattened on the side, inequilateral, truncate behind; valves rather 

 thick; beaks somewhat prominent, Undulate at the tip; epidermis striate, dark-brown, rayless; cardinal teetli 

 rather thick, compressed, oblique, acuminate ; lateral teeth long and curved ; nacre white. 



Hab. Oconee river, near Athens, Georgia. Major Le Conte. 

 My cabinet and cabinet of Major Le Conte. 

 Diam. .8, Length L3, Breadth 2.2 inches. 



Shell smooth, oblong, rather compressed, flattened on the side, inequilateral, truncate 

 behind, rounded before; substance of the shell rather thick, beaks somewhat prominent, 

 undulated at the tip and submedial; ligament rather long, thin and nearly covered; epider- 

 mis dark brown, without rays, thickly striate over the lower half of the shell, thick and 

 smooth above; lines of growth not well defined; posterior slope compressed into an 

 elevated carina, with a slightly impressed furrow, which has two very obscure raised lines; 

 umbonial slope rounded ; cardinal teeth rather thick, compressed, oblique, acuminate, 

 crenulate and double in both valves; lateral teeth long, curved and thickened at the pos- 

 terior end; anterior cicatrices distinct; posterior cicatrices confluent; dorsal cicatrices 

 placed nearly in the centre of the cavity of the beaks; cavity of the shell shallow and 

 wide ; cavity of the beaks shallow and obtusely angular ; nacro white. 



