MANSFIELD, MASS. — The Seyon Group has acquired a 350,000-square-foot warehouse in Mansfield for $38.5 million. Located at 560 West St., the Class A facility, which was built in 2009, is a cross-dock warehouse. Cross-dock warehouses are rare in the Greater Boston market, where high land costs have resulted in limited new warehouse construction. There are only 12 such facilities in Boston, according to the Seyon Group. This marks the 15th acquisition for the Seyon Group, which was launched in January 2017.