44 DESCRIPTION OF FIFTY-TWO SPECIES OF TJNIONID^. 



Unio rostellum. pi. 15, fig. 41. 



Testa Isevi, lata, compressa, ad latere planulata, valde insequilaterali, postice obtuse biangulari, antice 

 rotunda; valvulis tenuibus; natibus parvis ; epidermide tenebroso-fusca, obsolete radiata; dent- 

 ibus cardinalibus compressis, crenulatis, in utroque valvule duplicibus; lateralibus prselongis, 

 lamellatis rectisque ; margarita vel albida vel purpurea et valde irldescente. 



Shell smooth, wide, compressed, flattened at the sides, very inequilateral, ob- 

 tusely biangular behind, round before ; valves thin ; beaks small ; epidermis dark 

 brown, obscurely rayed ; cardinal teeth compressed, crenulate, double in both 

 valves ; lateral teeth very long, lamellar and straight ; nacre white or purple and 

 very iridescent. 



Proc. Acad. Nat. Sci., 1872, p. 160. 



Hah. — Macon, Georgia, J. C. Plant. 



My cabinet, and cabinets of Mr. Plant and Mr. Wheatley. 

 Diam. '6, Length 1, Breadth 2-6 inches. 



Shell smooth, wide, compressed, flattened at the sides, very inequilateral, ob- 

 tusely biangular behind, round before ; substance of the shell thin ; beaks small ; 

 ligament rather long, thin and dark brow.n, obscurely rayed, with indistinct, rather 

 distant marks of growth; umbonial slope obtusely angular; posterior slope slightly 

 carinate, very much compressed, with impressed lines from the tips to the posterior 

 margin; cardinal teeth compressed, crenulate, double in both valves; lateral teeth 

 very long, lamellar and straight ; anterior cicatrices distinct, large and slightly 

 impressed ; posterior cicatrices confluent, large and very slightly impressed ; dorsal 

 cicatrices placed above the centre of the cavity of the beaks : cavity of the shell 

 shallow and wide ; cavity of the beaks scarcely perceptible ; nacre white or purple 

 and very iridescent. 



Remarks. — Half a dozen specimens are before me, all of which were received 

 from Mr. Plant long since. I have delayed describing it in hopes of getting better 

 specimens, but have not succeeded. This species is near rostriformis (nobis), but 

 it is not quite so acute. It is a smaller species and more compressed. The figure 

 is probably from a female. It is near to exacutus (nobis), but is smaller and less 

 solid. The beaks of all the specimens are much eroded, but there are remains 

 which indicate a number of small undulations at the tips. 



Unio Irwinensis. PI. 15, fig. 42. 



Testa Isevi, suboblonga, parum compressa, ad latere parum planulata, valde insequilaterali, postice 

 obtuse biangulata, antice rotundata; valvulis subcrassis, antice crassioribus ; natibus prominulis, 

 ad apices undulatis ; epidermide olivacea vel fusca, obsolete radiata; dentibus cardinalibus sub- 

 grandibus, parum compressis, sulcosis, in utroque valvulo duplicibus; lateralibus longis, sub- 

 lamellatis subcurvisque ; margarita alba vel purpurea vel salraonis colore tincta et valde iridescente. 



