24 THE NAUTILUS. 



The third paper mentioned above is already so condensed that 

 any abstract is difficult to make. It deals with the questions of 

 classifications, mutual relationships of the genera, and geographic 

 distribution. Margaritana is merged in Unio, as the species are 

 believed to have lost the lateral teeth by degeneration or disease. 

 It is an error, however, to give U.margaritifer (nof'margaritiferus") 

 as type of Unio ; and it should be noted that in having a series of 

 small muscle-scars in the middle of the disk, M. mat-gar it ij'era, mon~ 

 fiilnnta, etc., differ from any Unios as well as from the M. undu/atu, 

 rugosa group, which is more properly called Alasmodonta. These 

 groups seem to be as valid genera as CaxtaHna, which Simpson re- 

 tains. Simpson, in common with other recent authors, recognizes 

 two families, Unionidce and Mi/telidce. The former containing gen- 

 era Unio, Anodonta, Prisodon, Tetraplodon, Castaliita, Burtonia, 

 Arconaia, Cristaria, Lepidodexma, (new genus for U. languilati of 

 China), Pseudodon, Leguminaia, Solenaia. Mutelidce contains 

 Muiela, Chelidonopsls, Spatha, I'leiodon, Brazzcea, Glabaris, Ihering- 

 ella, Monocondylwa, Fotsanla, Mycetopoda. Each genus is discussed 

 in a separate paragraph, and a careful reading inclines us to place 

 great reliance upon Mr. Simpson's conclusions. A full synonymy 

 of each genus would have been a useful addition, for there are some 

 generic names not mentioned in the text, probably because they 

 prove to be mere synonyms. 



The geographic provinces indicated by l/nionidce and Mutdidw 

 are: Palcearctic, including all Europe, Africa north of Sahara (ex- 

 cept the Nile), all northern Asia, and the Pacific drainage of North 

 America. Ethiopian. Oriental, including southern Asia to Japan, 

 Philippines, Malay Archipelago and to the Solomon Is. Anxtrnllitn, 

 Australia, Tasmania and New Zealand. Mississippian, the Gulf 

 drainage, spreading to N. C. and Central America. This region is 

 the richest in species in the world. Atlantic, Atlantic drainage from 

 Florida to Labrador. Neotropical, the whole of South America. 

 <'i titrtil American, Panama to Mexico and Cuba. A map presents 

 the areas of distribution graphically. In conclusion Mr. Simpson 

 discusses the geological history of the groups. Students of the 

 Uniones will find this paper crowded with important facts and care- 

 ful reasoning from them, in the main very reliable. Our experience 

 with other groups leads us to believe, however, that more import- 

 ant points will follow an anatomical study of the Uniones than have 

 yet been developed. 



