182 ON THE NAIADES, 



Unio dromas. Plate X. fig. 29. 



Testa subtriangulari, subobliqud, gibbd, irregulariter transversimque plicatd, 

 puncliunntlis passim radiata; valviilis crassissimis ; natibus prominent ibus ; 

 dentibiis cardinalibus lalis, lateralibiis crassis brevibusque ; mai'garitu alba. 



Shell subtriangular, somewhat oblique, hunch-backed, irregularly and transversely 

 folded, with dotted rays over the whole disk ; valves very thick ; beaks elevated ; car- 

 dinal teeth wide ; lateral teeth short and thick ; nacre pearly white. 



Hab. Harpeth River, Tennessee. Professor Conrad. 

 Hab. Cumberland River, near Nashville. Professor Troost. 



My Cabinet. 

 Cabinet of the Academy of Natural Sciences of Philadelphia. 

 Cabinet of Professor Troost. 

 Cabinet of P. H. Nicklin. 

 Diam 1-6, Length 1-8, Breadth 1-9 inches. 



Shell subtriangular, somewhat oblique, hunch-backed, irregularly 

 and transversely folded at the separate stages of growth, furnished with 

 an oblique furrow before the umbonial slope, substance of the shell 

 very thick ; beaks thick and elevated ; ligament short, thick and dark 

 coloured; umbones furnished with a hump; epidermis yellow, with 

 numerous dark green dotted rays, on the anterior part furnished with 

 about six somewhat broad rays; cardinal tooth wide and sulcate ; lateral 

 tooth short and thick, having a flat plate between it and the cardinal 

 tooth ; anterior and posterior cicatrices both distinct ; dorsal cicatrices 

 situated on the under side of the cardinal tooth ; cavity of the beaks 

 deep and angulated ; nacre pearly white, on the posterior part some- 

 times golden. 



Remarks. — I have had for some years in my cabinet two specimens 

 of this beautiful and curious species, the first of which, a young one, I 

 owe to the kindness of the late professor Conrad. Having recently 

 received a complete suite from professor Troost, I have perfectly satis- 

 fied myself of (what I before doubted) its being distinct from the 

 irroratus (nobis). The manner in which the hump is formed is very 

 remarkable. As far as the third or fourth stage of growth the disks 



