How large was the largest known fossil lamp shell?

The largest known fossil lamp shells (brachiopods) were relative giants, measuring approximately 38 centimeters (15 inches) wide.1

It is important to note that lamp shells (phylum Brachiopoda) are distinct from branchiopods (a group of crustaceans) and brachiosaurs (a genus of dinosaurs), which are often confused due to similar-sounding names. While some fossil brachiopods reached these significant sizes, most species are much smaller, typically measuring 2.5 centimeters (1 inch) or less in length or width.2341