ZOOLOGY. 379 



brought by Dr. Cooper, were exhibited by Mr. Lea, which were of exquisite 

 purple and salmon. The Unio ligament inns has probably never been found 

 pink or purple in the Ohio; while at Grand Rapids, Mich., those with a tine 

 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, Connec- 

 ticut, and Massachusetts are almost universally white, as those from the 

 northern part of Europe are aiso. 



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 substance in their composition. The subject was certainly one well 

 Avorth the pursuit, as no doubt could remain that the color was derived from 

 some foreign substance entering into the composition of some individuals, 

 while others Avere free from it. It was not an uncommon case to find the 

 dorsal portion of the nacre to be pink or purple, Avhile the other portions 

 were Avhite; and this was also sometimes the case Avith the caA-ity of the 

 beaks. Mr. Lea did not believe the color arose, as some persons supposed, 

 from the structure of the surface of the nacre d'mding the rays of light by 

 thin laminations. This division of color Avas exhibited in almost eA^ery 

 species, and is Avhat 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 composing the substance of the valves. 



ON THE NUMBER OF THE UNIONIDJ3 IN THE UNITED STATES. 



At a recent meeting of the Philadelphia Academy, Mr. Isaac Lea gave the 

 folloAving statement respecting the number of the Unionidce in the United 

 States : 



Unio, ....... 465 species. 



Margaritana, ..... 26 " 



Anodcmta, . . . . . 59 " 



550 

 To these may be added new species in his cabinet 



not yet described, .... 30 



580 



And to these may be added, for North America, 

 knoAvn to inhabit Mexico, Honduras, Cen- 

 tral America, and one in Canada, 



Unio, .... 29 



Auodonta, . . . .8 



37 



617 



Mr. Lea further observed that we have not in North America either of the 

 genera Triquctra (Hyria, Lam.), Prisodon (Castalia, Lam.), Monocwtdylaa, 

 Mycctopus, Byssandonta, or Plogiodon. They are all emphatically South 

 American types, while there does not seem to inhabit the southern half of 

 America a single species of Margaritana (Alasmodonta, Say.). Ferussac has 

 described a species (A. incurra} as coming from South America, but there is 

 reasonable doubt of it. The Monocondylcea and Margaritana seem mutually 

 to replace each other. The Uniones and Anodontai prevail in both parts of 



