Under the heading "Ordovician Crustacean Leg," Walcott (1918, p. 154, pl. 36, figs. 1,2) has recently redescribed these specimens, and thinks that they do not belong to _Calymene_, nor, indeed, to any trilobite. He concludes that they were more like what one would expect in an isopod. Passing over the fact that the oldest isopod now known is Devonian, the fossils in question seem to me quite trilobite-like. Walcott says: The legs are associated with fragments of _Calymene meeki_ but it is not probable that they belong to that species; if they did, they are unlike any trilobite leg known to me. The very short coxopodite and basopodite are unknown in the trilobites of which we have the legs, as they are fused into one joint forming the long protopodite in the trilobite. The distal joint is also unlike that of the trilobite legs known to us. A great deal of Doctor Walcott's difficulty probably arises from his homology of the coxopodite of the trilobite with the protopodite of the higher Crustacea. The coxopodite of the trilobite is not fused with the basipodite, this latter segment always remaining free. Indeed, Walcott himself says of _Neolenus_ (1918, p. 128): Each thoracic leg (endopodite) is formed of a large elongate proximal joint (protopodite), four strong joints each about 1.5 times as long as wide (basopodite, ischiopodite, meropodite and carpopodite); two slender elongate joints (propodite and dactylopodite) and a claw-like, more or less tripartite termination. Walcott's drawing (pl. 36, fig. 1) is a composite one, and while it shows eight segments, I was not able to count more than seven on any of the specimens themselves. In regard to the terminal segment, the dactylopodite of the limb shown in his plate 36, figure 2, is unusually long, and a comparison with other photographs published on the same plate shows that such long segments are unusual. Proof that these are appendages of a _Calymene_ is of course wanting, but there is no particular reason so far to say that they are not. _Measurements:_ Two of the more complete specimens, each showing six segments, are each 8 mm. long. Somewhat similar to the specimens from Covington are the ones described by Eichwald (1825, p. 39, 1860, pl. 21), the specimens being from the Silurian of Gotland. The figure copied by Walcott (1881, pl. 6, fig. 4) has never been looked upon as entirely satisfactory evidence of the nature of the specimen, and so far as I know, the fossil has not been seen by any modern investigator. =Ceraurus pleurexanthemus= Green. (pl. 11; text figs. 12, 17-19, 21, 22, 24, 29, 30.)