other authors taken up this problem as far as we are aware. In several species we have found distinct openings in the corners where the posterior points of the triangular areas of the opercular plates meet the lateral points of the hastate basal portion in the unpaired lobe of the female genital appendage. These lateral points are as a rule extended into earlike or scroll-like lobes that cover the openings. Since the paired interior tubular appendages observed in Eurypterus end at these lateral points, it is certain that they emptied here, as suggested by Holm, who considers them as auxiliary generative organs.
The large opercular appendage of the female is but a median tongue and not a tube, and it is probable that it concealed the complicated terminal portions of the genital organs, as the median part of the operculum still does today in the arachnids Phrynus and Thelyphonus. Gaskell [p. 192] has drawn a restoration, representing these genital organs "in accordance with our knowledge of the nature of these organs in the present-day scorpions, as a median elongated uterus, bilaterally formed, from which the genital ducts passed, probably as in Limulus, towards a mass of generative glands in the cephalic region, and not as in Scorpio or Thelyphonus, tailwards to the abdominal region." We surmise that the female eurypterid thrust this chitinous opercular appendage, together with the opercular plate, into the sand during oviposition, just as Limulus does today.
It is possible that the paired tubular organs mentioned above are not auxiliary generative organs, as surmised by Holm, but are the genital ducts and that the openings observed by the writers are the apertures of these ducts leading into the median uterus.
The sternal plates of the third to the sixth mesosomatic somites are well developed, forming the four sternites following the operculum. These plates are always slightly arched forward, the anterior margin being slightly convex, the posterior concave. The antelateral angles are produced into rounded lobes and the median line is marked by a suture, along which they readily separated. The sternites were often more arched than the
