410 GEOLOGICAL SURVEY OF THE TERRITORIES. 
¥ia@. 38.—Actual section through the head of Limulus, showing the second pair of appendages and 
their relations to the shell or carapace: ht, heart; liv, liver; end, appendage homologous with the en- 
dopodite of Decapoda. ; 
Fic. 39.—Dinagrammatie section through body 
of a hypothetical form to show the possible ho- 
mologies between the appendages of Limulus and 
a trilobite; the lettering as in Fig. 40. 
Fic. 40.—Restored seetion of the thorax of a 
trilobite (Calymene) after Walcott: c, carapace ; 
en, endopodite; en’, exopodite, with the gills 
on the exopodal or respiratory part of the ap- 
pendage. 
