22 
useful and ingenious researches, that the 
irregularities of the external shells in the 
living species of crustaceans have a constant 
relation to distinct compartments in their in¬ 
ternal organisation, and by the application of 
these distinctions to fossil species, he has been 
enabled to draw some highly curious, novel, 
and important conclusions respecting their 
internal and general structure. From my 
limited knowledge of the anatomy and the 
habits of our living crabs, I would merely 
suggest, that the peculiar organ in the animal 
economy of the trilobite, which the gullar 
plate above described was intended to inode! 
and protect, was perhaps the stomach , and that 
the spaces on each side of it covered the 
anterior portions of the liver> 
The upper shell of the genus calymene, 
like that of the isotelus and dipleura, natural¬ 
ly and obviously divides itself into three parts, 
the buckler or shield—the abdomen and the 
caudal end. This last portion in the caly¬ 
mene is not covered with a thick epidermis, as 
in the two genera above mentioned, the articu* 
