AND OTHER FAMILIES. 99 



Poland, Ohio. It is very nearly allied to the snbrotunilus (nobis), and 

 when I first received a few s}3ecimcns, I doubted if it was more than 

 a variety of that species. Subsequently receiving from the same natu- 

 ralist more and better specimens, I was satisfied that it was specifically 

 different. Specimens of the true siibrotundits having accompanied 

 these, it could not be, of course, a variety occasioned, as is sometimes 

 the case, by mere locality. It dillers from the subrotundus in being 

 much flatter, in having smaller beaks, and in being of a darker brown — 

 the beaks are less yellow — the rays, interrupted like that shell, tend 

 generally nearer to the margin. In older specimens than the one 

 figured, the posterior part becomes protruded, which gives an oblique- 

 ness to the shell. 



Unio Pauanensis. Plate XIV. fig. 42. 



»• 



Testa siihrotundatu, inxquilutcruU, compressd ; valimlis sithcrassis ; natibus 

 plicatis relusis ; dentibus cardinalibus recurvis, in valvuld ictruque duplicibus ; 

 lateralibus sublongis curvisque ; margaritu albd et iridescenie. 



Shell subrotuntl, inequilateral, compressed; valves somewhat thick; beaks folded, 

 retuse ; cardinal teeth recurved, double in both valves ; lateral teeth rather long and 

 curved ; nacre pearly white and iridescent. 



Hab. River Parana. Dr Burrough. 



Cabinet of Dr Burrough. 

 Diam. 1*3, Length 3, Breadth 3-5 inches. 



Shell subrotund, disposed to be pentagonal, inequilateral, compressed 

 towards the margin, emarginate on the posterior dorsal margin ; um- 

 bonial slope flattened ; substance of the shell somewhat thick ; beaks 

 rather elevated, longitudinally folded, retuse ; ligament rather long and 

 thin ; epidermis wrinkled, shining, greenish on the beaks and brown 

 towards the margin, furnished with very obscure curved rays, which 

 sweep from the beak towards the anterior part ; cardinal teeth recurved, 

 compressed, double in both valves; lateral teeth lamellar, rather long 

 and curved ; anterior cicatrices confluent ; posterior cicatrices confluent ; 



