1& 



On the Homologies of the Cn 



Limb. [October, 



as regards their thoracic limbs, do not remotely resemble the 

 abdominal limbs of Limulus. In this connection we would draw 

 attention to Fig. n, which is designed to show the possible rela- 

 tions between Limulus and Calymene, or the Merostomata and 

 the Trilobita. The essential difference is in the nature of the 



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limbs ; the thoracic limbs of trilobite, while having a jointed endo- 

 podite as in Limulus, also having an exopodite and a forked 

 spiral gill. Now, if we append to the coxopodite of Limulus an 

 exopodite, and instead of having the gills arranged anteroposte- 

 riorly, like the leaves of a book, have them arranged on one side 



