NO. 6 ANNELIDA, ON YCHOPHORA, AND ARTHROPODA SNODGRASS II3 



arthropods some of the adductor fibers of the mandibles go con- 

 tinuously from one appendage to the other. 



That the prosoma of Limulus contains at least a part of the eighth 

 somite is evident from several structural features, but the writer's 



Fig. 48. — Structure of Chelicerata and Trilobita 



A, Liobunum sp. (Phalangida), anterior view of body, showing secondary 

 preoral position of chelicerae above base of labrum. B, same, "endosternite" 

 of prosoma with adductor leg muscles (suspensory dorsal muscle not shown). 

 C, Limulus polyphevms Linn. (Xiphosurida) , section of prosoma behind third 

 legs, leg muscles somewhat diagrammatic. D, diagrammatic cross-section of 

 a trilobite. E, Limulus polyphemus, fourth leg, with coxal epipodite. F, same, 

 base of a left leg, mesal view, with muscle insertions (from Benham, 1885). 



a, dorsal articulation of coxopodite ; b, ventral end of coxal axis ; Bud, basen- 

 dite ; Chi) chelicera ; Cp, carapace ; Cxpd, coxopodite ; D, dorsum ; dbl, doublure ; 

 dO, dorsal ocellus ; E, lateral eye ; Eppd, epipodite ; /, tergal promotor muscles 

 of coxopodite ; J, tergal remotors of coxopodite ; K, anterior ventral muscles of 

 coxopodite ; k, ligamentous "endosternite" on which ventral leg muscles are at- 

 tached ; L, posterior ventral muscles of coxopodite ; 3L, third leg ; Lm, labrum ; 

 Pdp, pedipalp; Tlpd, telopodite; t-s, tergal suspensory muscleof "endosternite"; 

 V, venter ; 26, 2/, dorsal promotor muscles of coxopodite arising on carapace ; 

 2^, 28, 2g, dorsal remoter muscles arising on carapace ; 32m, 32n, anterior and 

 posterior branches of coxal adductor arising on "endosternite" ; 33, 34, ventral 

 remotor and promotor muscles arising on "endosternite". 



former statement (1936) that the prosoma and opisthosoma of 

 Limulus are separated between segments VIII and IX is not strictly 

 correct. The attachment of the muscles and the distribution of the 

 nerves in this region demonstrate that the dorsal hinge between the 

 prosomatic carapace and the opisthosomatic carapace lies within the 



