Page:Smithsonian Miscellaneous Collections, Volume 85.djvu/123

Rh 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 beside it extending out from the end of the joint. The anterior legs appear to have been delicate and slender, but 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 second 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 trilobite Triarthrus becki.



On some specimens showing the expanded joints the extended portion is very 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 prevailing 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 ventral side of the endopodite is buried 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