I found a better reference.
In ,page 24, 

Theoretically, polygamy can assume any one of three possible forms: polygyny or the marriage of one man to two or more wives at a time, polyandry or the coexistent union of one woman with two or more men, and group marriage or a marital union embracing at once several men and several women.  Of these, only the first is common.

And on page 25 

A statistical analysis of Kaingang genealogies for a period of 100 years showed that 8 per cent of all recorded unions were group marriages, as compared with 14 per cent for polyandrous, 18 per cent for polygynous, and 60 per cent for monogamous unions.

The disadvantage of working at a medical school is that the anthropology texts are not extensive, but they aren't checked out often either. This had been sitting on the shelf for over 20 years, deep in the recesses of the basement. Murdock is a sufficient reference for polygamy including group marriage.