21 
for the purpose of defence, then the gullar 
plate being composed of a single piece, and 
therefore not contractile, reached below the 
fourth articulation of the back. Some of our 
specimens illustrate this conformation in a 
very satisfactory manner. None of our frag¬ 
ments exhibit fairly the small surface on each 
side of the gullar plate, and the edge of the 
buckler beneath the eyes. This space was 
probably slightly concave, and occupied with 
the mandibles and their palpi, as in the genus 
serolis—the mouth being no doubt placed 
near the rounded termination of the gullar 
pouch. 
Thus we have at last discovered nearly the 
whole inferior surface of the buckler of the 
genus calymene, a portion which includes 
about one third of the animal. Not the 
slighest impression or other vestige of anten- 
nse can be perceived, and we may therefore 
pretty confidently conclude, that this genus 
of triiobites was destitute of those organs. 
Professor Demarest, in his history of fossil 
Crustacea, seems to have ascertained by his 
