two slender distal joints. Each joint has one or more short, sharp spines curving forward from the outer end, and the terminal joint has two large and one small forward-curving spines not unlike the spines on the terminal joints of the cephalic appendages of Eurypterus. In other specimens the exopodite appears to be in the form of a lobe or lamellæ not unlike the branchial lobes of Pterogotus bilobus as illustrated by Dr. Henry Woodward.[1] The branchial appendages of Sidneyia are illustrated in my paper on Middle Cambrian Merostomata.[2]
 Fig. 10.—Sidneyia inexpectans Walcott. ✕ 3. Flattened dorsal shield with 4 pairs of cephalic appendages, and jointed setiferous thoracic legs. |
The discovery of the jointed body legs of Sidneyia strengthens the conclusion reached in 1911, that Sidneyia was a transition form between the Trilobita and Eurypterida.
The accompanying text figure illustrates one of the specimens of Sidneyia showing the jointed body appendages.
For description of mode of occurrence and locality, see original description.
- ↑ Monogr. British Fossil Crustacea, Order Merostomata, 1866-1878; Pal. Soc. London; Pl. 12, figs. 1a and 1d.
- ↑ Smithsonian Misc. Coll., Vol. 57, No. 2, 1911, pl. 6, fig. 3, and pl. 7, fig. 1.
