AND OTHER FAMILIES. 67 



on the posterior part ; cardinal teeth double in both valves, compressed 

 and erect; lateral teeth very long, thin and nearly straight; anterior 

 cicatrices distinct ; posterior cicatrices confluent ; dorsal cicatrices situ- 

 ated in the cavity of the beaks ; cavity of the beaks very small ; nacre 

 beautifully pearly and iridescent. 



Remarks. — This is perhaps the most extraordinary Unto that has 

 yet fallen to the lot of a naturalist to describe. When we cast our 

 eyes ovei' all the species, and then rest them on this, we shall be ready 

 to exclaim, that nothing hereafter belonging to this genus can astonish 

 us. Its latitude is so great, that one at first sight can scarcely believe 

 it to belong to the family Naiades. Its great transverseness causes the 

 lateral teeth to be exceedingly long, and that character, together with 

 the acutely angular posterior margin, gives the shell the form of a 

 crane's beak. In outline it does not approach any species I know, and 

 therefore there can be no comparison made. I procured it of a dealer 

 in London, and dedicate it to my friend, John Edward Gray, Esq. of 

 the British Museum, one of the most distinguished naturalists in Great 

 Britain, and to whose great kindness and attention while in London I 

 am much indebted. I know of no zoologist who has, in that country, 

 pursued our favourite science with more ardour or more success, and 

 it is only due to him, while it gives me great pleasure to render him 

 this tribute of respect in placing his name to one of the most inte- 

 resting species of the whole family. 



Unio Burroughianus. Plate X. fig. 27. 



Testa suhrotunda, inxquilaterali, compressd, postice sttbangulata ; nalibus obli- 

 que plicatis, prominulis ; valvulis subcrassis ; epidermide tenebroso-fuscd ; dentibus 

 cardinalibus magnis, elevaiis el laminaiis, laterulibus subrecfis ; margaritd alba 

 et iridescente. 



Shell subrotund, inequilateral, compressed, subangular behind, with oblique folds on 

 the beaks ; valves rather thick ; beaks somewhat elevated and much plicate ; epidermis 

 dark brown ; cardinal teeth large, elevated and lamelliform ; lateral teeth nearly straight; 

 nacre pearly w^hite and iridescent. 



