208 NEW UNIONIDiE OF THE 



compressed, flattened at the sides, nearly equilateral, subbiangular and emarginate 

 behind, rounded before ; substance of the shell rather thick, slightly thicker be- 

 fore ; beaks somewhat elevated, pointed and beautifully undulate at the tips ; ligament 

 rather short and somewhat thick and light brown ; epidermis greenish yellow, sub- 

 striate, obscurely radiate or without rays, somewhat shining and with very distant 

 marks of growth ; umbonial slope slightly raised, obtusely angular and covered with 

 nodes ; posterior slope carinate, almost raised into a wing, covered with a series of 

 nearly parallel, curved rows of elongated tubercles wider apart a.t the approach to the 

 margin, depressed so as to cause a slight emargination ; cardinal teeth rather large, 

 compressed, oblique, erect, striate and double in both valves ; lateral teeth straight, 

 rather long, oblique and enlarged towards the end ; anterior cicatrices distinct, rather 

 large and well impressed ; posterior cicatrices confluent, large and slightly impressed ; 

 dorsal cicatrices placed along the base of the cardinal tooth and above the cavity of 

 the beaks; ventral cicatrices nearly in the centre of the disk and indistinctly 

 marked ; cavity of the disk very shallow and wide ; cavity of the beak deep and 

 angular ; nacre silver white and iridescent. 



Bemarhs. — Some time since I received two young specimens of this beautiful 

 species from Prof. Forshey, and now have several adult and perfect specimens from 

 the Smithsonian Institution. Hitherto I had doubts as to this being only a variety 

 of Forsheyi, but these specimens from the Smithsonian Institution are conclusive as 

 to their being specifically distinct. They are constant in the more quadrate form, in. 

 the smaller tubercles which might almost be considered granules, in the elevated 

 carina and the more compressed form. I know of no species which is so much 

 covered with small tubercles as this, except apiculatus, Say. Towards the tips these 

 sometimes arrange themselves in rows, gracefully finishing off the points. In all the 

 specimens before me the cicatrix of the ventral muscle is more or less obvious, while 

 in a dozen of Forsheyi before me, there are none visible. There are many affinities in 

 speciosm with Mr. Say's beautiful apiculatus, from Louisiana, which has, perhaps, the 

 most highly ornamented exterior of any of our Uniones. It need not, however, be 

 confounded with that shell, as it is more compressed, more transverse, and has smaller 

 tubercles and a less elevated umbonial slope. 



Unio Gerhardtii. PI. 31, fig. 277. 



Testa subsulcata, elliptica, subcompressa, sublenticular!, insequilaterali, postice obtuse angulata, antice 

 rotunda,; valvulis crassiusculis, antice paulisper crassioribus ; natibus subelevatis; epidermide 

 straminea, radiis capillaribus ; dentibus cardinalibus parviusculis, compressis, in utroque valvulo 

 duplicibus ; lateralibus sublongis, laniellatis subcurvisque ; margaritS, alba et valde iridescente. 

 Shell slightly sulcate, elliptical, rather compressed, sublenticular, obtusely an- 

 gular behind, round before ; valves somewhat thick, slightly thicker before ; beaks 

 somewhat raised ; epidermis straw yellow, with capillary rays ; cardinal teeth 



