298 R. 1. POCOCK. 



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 interpre- 

 tation 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 (exceptin L. rotundicauda) 

 the fifth segment, according to this new method of enumei'a- 

 tion, 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 PalEeophonus possessed any structures com- 

 parable to the pedal spurs of recent scorpions and to the 

 lobate sclerites of Limulus is doubtful. I can detect 

 nothing compai^able 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 



