Page:The Eurypterida of New York Volume 1.pdf/147

 dealt with by Laurie. Lankester had already indicated the close homologies existing in the number of body segments of the cephalothoracic appendages [see especially op. cit. tabular statements p. 536]. From these it would follow that Limulus on the one hand, Scorpio and the eurypterids on the other, separated before the consolidation of the body segments observable in Limulus; but Laurie states that the second abdominal segment in Scorpio is well developed and shows no sign of ever having been suppressed by the genital operculum as in the eurypterids. From this argument only it might seem that the scorpions came off the eurypterid stem before the great development of the genital operculum. Laurie considers this development of the genital operculum at the expense of the second free segment as a point of considerable morphological importance and has therefore [op. cit. 526, see also Recent additions, etc. p. 127] considered it probable that the Pedipalpi (Thelyphonus) are more nearly allied to the eurypterids than are the scorpions, for in the former a similar suppression of the second ventral segment has taken place in favor of the genital plate. The four scorpions known from the Siluric all exhibit