I am involved in looking at mussels from Late Woodland (circa AD900 to 1600)
Native American sites in the Delaware Valley of Pennsylvania and New Jersey.
Mussels are most well represented in understandable contexts from the upper
portions of the Delaware Valley. Bill Lellis, a specialist at the USGS
Leetown Science Center, was surprised at the relatively small size of the
mussels from archaeological contexts. One of the potential explanations for
this pattern is that the smaller less mature mussels are more palatable than
older and larger ones. A data sample is below.

Faucett Site: Feature 207 contains mussel shells in the 100s. Mussels range
in size from 4.1cm x 2.1cm, 4.8cm x 2.7cm, 5.4 cm x 3.1cm; Feature 295:
Mussel shells are numerous (1000s) and range from a highly fragmented
condition to 3.7cm x 2.4cm, 4.3cm x 2.5cm.
The modern mussel sample from nearby portions of the river measures 10.8cm x
5.8cm

Depue Island Site: Archaeological Samples: 2.9cm x 1.5cm; 3.0cm x 1.6cm;
3.7cm x 2.2cm; 4.0cm x 2.45cm.  Modern samples from nearby portions of the
river measure 6.3cm x 3.5cm to 7.6cm x 4.0cm

Kutay Site: Feature 75 contained 3,650 mussels (31 lbs., 11 oz.) that ranged
in size from 0.7" to 2.3" in length (1.5" mean) and was one of the five
largest shell filled pits on-site (Kinsey 1972: Table 9, 253). My
measurements show a size  range from 3.7cm x 2.1 cm to 4.0cm x 2.2 cm.
Modern mussels range in size from 9.1cm x 4.8cm to 9.6cm x 5.1cm.

Michael Stewart
Department of Anthropology
Temple University
Philadelphia, PA 19122