454 MEMOIRS OF THE CARNEGIE MUSEUM. 



Superfamily NAIADES. 



I. Family Margaritanid^e Eurasia and Nortli Aniorica (discontimious). 



II. Family Unionid-e: 



1. Subfamily Unionin* Eurasia, Africa, Nortii Aincrica, soutlnvard to ("outral America. 



2. Subfamily Anodontin.e Eurasia, North America, southward to Central America. 



3. Subfamily Lampsiun.« North America southward to Mexico. 



III. Family Mutelid.e: 



L Subfamily Hyriin.e South America (but not in Central America), Australia. 



2. Subfamilj' Mutelin.e South America to southern Mexico, Africa. 



I can not improve upon this arrangement at present. It possibly might be 

 advisable, in future, to elevate the two South American subfamilies to the rank of 

 families, but I refrain from doing this, chiefly because the African and Australian 

 forms belonging to them are too poorly known. The fact that in South America 

 two groups of Naiades are found, which are more closely allied to each other than 

 to any other group, is well expressed by uniting them into one family {Mutelida). 



The more primitive subfamily, Hyriince, is found all over South America, but 

 becomes rare in the northern parts (Venezuela and Colombia), and is missing, so 

 far as known, in Central America. It is quite abundant in Chile, where the Mu- 

 telinm are absent, and it is also found in Australia. - 



The more specialized group, subfamily Mutelince, is found in South America, 

 east of the Andes. It is missing in C-hile, but has been reported from the Pacific 

 drainage in Ecuador. It goes into Central America and reaches southern Mexico. 

 On the other hand it is represented in Africa, probably all over the continent, 

 with the exception of the Mediterranean region. 



This geographical distribution of the larger groups is extremely significant, 

 for it serves to support certain theories as to the origin of the South American 

 continent, its former connections, and the origin of its fauna. The presence of 

 the Hyriince both in South America and Australia indicates the former connection 

 of both continents, probably by way of Antarctica, and the fact that species of 

 Diplodon, the most primitive of the South American Hyriince, are found in Chile, 

 is entirely in keeping with this. The fact that Unionida' with certain Hyriinc 

 structures^ are found chiefly in southeastern Asia, su'ggests that thej^ probably 



^ It is unknown whether all the Australian Naiades belong here. Unionida; related to the Hyriince 

 in having the septa of the marsupium interrupted, are known to me from southeastern Asia (Siam, 

 China) and northwestern America (Pacific slope), but these forms certainly are Unionidm in all other 

 respects. 



' Interrupted septa in the marsupium are known in the Asiatic Unioninw: Lomrllidcns (Ortmann, 

 lOllo, p. 100); in llyriopsis and Coniradrns (Ortmann, Nautilus, XXX, 1910, pp. 85 and 100); and, 

 according to the figures of Haas (System. Coufhyl. Cai)in., XIX, 1911 and 1912), also in Reclidens and 

 Aeuiicosla. 



