half with a sutural impression, which represents, I believe, the line of union between two segments, the portion on the proximal side of the line being the fourth, that on the distal side the fifth segment of the appendage. If this interpretation be correct there is the same number of segments in these appendages in both Limulus and the scorpions. Now in the fourth leg of Limulus (except in L. rotundicauda) the fifth segment, according to this new method of enumeration, is furnished beneath distally with a spur like those described above in the scorpions. Again, at the extremity of the sixth segment in Limulus there are four moveable lobate sclerites, which spread out like the fingers of a hand when the leg is plunged into the mud. At the extremity of the sixth segment in the scorpion's leg, or rather on the arthrodial membrane between it and the seventh, there are either one or two "pedal" spurs, which represent, I suggest, the lobate sclerites in the same position on the leg of Limulus. Lastly, there is attached to the distal extremity of the seventh segment in Limulus a pair of short moveable sclerites, forming a small nipper. Similarly there is a pair of moveable sclerites or claws articulated to the distal extremity of the seventh segment in the scorpion's leg. The annexed figure (Fig. 2) will make these suggested homologies clear.
Whether Palæophonus possessed any structures comparable to the pedal spurs of recent scorpions and to the lobate sclerites of Limulus is doubtful. I can detect nothing comparable to them in the Scottish specimen, but the figure of the Gotland specimen suggests the possibility of the presence of one or more spurs at the distal end of the sixth segment.
It is a matter for regret that the exact structure of the basal segments of the legs, and the relation of these segments to one another, are not with certainty interpretable, owing to the crushing and displacement of the parts composing the ventral area of the prosoma, and of the anterior somites of the mesosoma. Hence too much reliance must not be placed
