28 
would still retain nearly a rectilinear position; 
thus no interference would occur in the ordi¬ 
nary functions of the animal economy when 
the body was contracted. 
Besides the organs of locomotion and respi¬ 
ration beneath the abdominal arches of the 
genus calymene, it is probable that on each 
side of the deep cavity under the caudal end 
there was placed a series of thin transverse 
plates, which also performed the combined 
functions of breathing and swimming : a simi¬ 
lar disposition of laminated branchiae may 
be observed also in the limulus and in the 
serolis. Beneath this deep cavity the heart 
of the animal was also probably placed. 
What we have said with regard to the 
inferior mechanism of the trilobite, applies 
exclusively to the genus calymene. It is pro¬ 
bable that this structure differs essentially in 
all the genera of this remarkable family. Dr. 
Dekay has described and figured in the first 
volume of the Annals of the Lyceum of Na¬ 
tural History of New York , the under side of 
the buckler of the isotelus, which is very pe» 
