NO. 



BURGESS SHAI,E FOSSILS WALCOTT 



33 



sides ; narrow and slender on the dorsal and ventral view ; short, very 

 fine spines occur at their distal end and along the side of the joints. 

 The slender distal joint is more nearly cylindrical and has a short, 

 strong, slightly curved spine with one or two fine spines heside it ex- 

 tending out from the end of the joint. The anterior legs appear to have 

 been delicate and slender, hut usually they have retained their natural 

 position remarkably well. Usually the first joint of the endopodite 

 of the fourth pair of limbs is slightly expanded, and the first and sec- 

 ond joints of the fifth to seventh pairs of limbs, and the first five joints 

 of the eighth to twentieth pairs of limbs. The expanded joints vary in 

 degree of expansion from slight enlargement on the fourth limb to 

 where the transverse diameter is considerably greater than the length 

 of the joint. The latter recall the transverse flattened joints of the 

 endopodite of the trilobitc Triarthnts hecki.^ 



Fig. II. 



-Diagrammatic enlargement of a section of the exopodite showing the 

 bodv and the attached cylindrical filaments. 



On some specimens showing the expanded joints the extended por- 

 tion is A'ery narrow from base to point, and gives the effect of a strong 

 spine projecting from midway of the joint ; in other specimens the 

 base is as long as the joint and the apex is obtuse, which is the pre- 

 vailing form. When in a natural condition the expansion of the joint 

 was undoubtedly on the lower or the ventral side, and the fact that 

 in the fossil state specimens occur with all the expansions pointing 

 forward means only an accident of preservation ; some occur with 

 scarcely a trace of the enlarged joint, owing to the fact that the ven- 

 tral side of the endopodite is l)uried in the shale, leaving the narrow 

 dorsal side in view; in the restoration (fig. 9) I have outlined the flat, 

 vertical posterior side of the endopodite. 



Exopodite. — The exopodite is attached to the protopodite about 

 midway of the length of the latter. It is formed of a long, strong 

 proximal joint to which is attached a long, slender, multi-articulate 

 appendage, each segment of which supports a long, slender, flat 



^Smithsonian Misc. Coll., vol. 57, p. 13". pl- 30, fig. -'O, 1912. 



