206 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 5/ 



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 Euryp- 

 terus. In other specimens the exopodite appears to be in the form of 

 a lobe or lamellae not unlike the branchial lobes of Pterogotus bilobus 

 as illustrated by Dr. Henry Woodward,^ The branchial appendages 

 of Sidneyia are illustrated in my paper on Middle Cambrian Mero- 

 stomata.^ 



Fig. 10. — Sidneyia inexpectans Walcott. X 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; PI. 12, figs. la and id. 

 * Smithsonian Misc. Coll., Vol. 57, No. 2, 191 1, pl. 6, fig. 3, and pl. 7, fig. i. 



