NATURAL SCIENCES OP PHILADELPHIA. 89 



great lakes from the southern side, is very true. The Unio rectus is usually 

 white in the Ohio, though sometimes tinted with purple and salmon color, while 

 in the more northern waters it is usually of a fine rich purple or salmon. Two 

 specimens from the upper Mississippi, brought by Dr. Cooper, were exhibited 

 by Mr. Lea, which were of exquisite purple and salmon. The Unio ligamentinus 

 has probably never been found pink or purple in the Ohio, while at Grand 

 Rapids, Michigan, those with a fine pink and salmon color are very common. 

 The Margaritana margaritifera of Columbia river and its tributaries has a fine 

 purple nacre in almost all the specimens, rarely white, while those in the rivers 

 of Pennsylvania, Connecticut and Massachusetts are almost universally white, 

 as those from the northern part of Europe are also. 



Dr. Draper had informed Mr. Lea that he had calcined some of these purple 

 shells, but that they had burned white and he had not detected any metallic sub- 

 tance in their composition. The subject was certainly one well worth the pursuit, 

 as no doubt could remain that the color was derived from some foreign sub- 

 stance entering into the composition of some individuals, while others were 

 free from it. It was not an uncommon case to find the dorsal portion of 

 the nacre to be pink or* purple while the other portions were white, and this was 

 also sometimes the case with the cavity of the beaks. Mr. Lea did not believe 

 the color arose, as some persons supposed, from the structure of the surface of 

 the nacre dividing the rays of light by thin laminations. This division of 

 color was exhibited in almost every species, and is what naturalists call the 

 " pearly hue," oftentimes of great beauty, but quite a different matter from 

 the pink, purple and salmon color of the mass of the carbonate of lime com- 

 posing the substance of the valves. 



March 27th. 



Mr. Lea, President, in the Chair. 



Forty-eight members present. 



The following papers on report of the respective committees were 

 ordered to be printed in the Proceedings : 



Descriptions of Four New Species of TJNIONIDiE from Brazil and Buenos Ayres. 



BY ISAAC LEA. 



Unio trifidus. Testa lrevi, obliquo-oblonga, ad latere planulata, valde in- 

 nequilaterali, postice acute angulata, antice rotunda ; valvulis crassiusculis, 

 antice crassioribus ; natibus prominentibus, ad apices rugose et divaricate un- 

 dulatis ; epidermide micante, luteo-virldi, eradiata; dentibus cardinalibus 

 grandibus, trifidis, sulcatis ; lateralibus longis, crenulatis, in valvulo dextro 

 trifidis ; margarita, argentea et iridescente. 



Hab. Buenos Ayres, South America. M. D'Orbigny. 



Unio patelloides. Testa laevi, subrotunda, subcompressa, subeequilaterali, 

 antice et postice rotundata ; valvulis subcrassis, antice crassioribus ; natibus 

 prominulis, ad apices divaricate undulatis ; epidermide tenebroso-castanea, 

 striata,, eradiata; dentibus cardinalibus longis, compressis, obliquis, crenulatis 

 corrugatisque ; lateralibus longis, crenulatis curvisque ; margarita argentea 

 et iridescente. 



Hab. Amazon River, Brazil. Captain George Brown. Rio Plata. H.Cum- 

 ing. 



Anodonta Amazonensis. Testa. Isevi, transversa, subinflata., valde insequi- 

 laterali, postice subbiangulata, antice rotunda; valvulis subcrassis; natibus 

 I860.] 



