tion which rests in the basal segments termed coxae. In correspondence with this activity these are narrow, elongate, subtriangular, armed with rows of teeth borne on the narrow end (gnathobase or mandible) and form a manducatory edge. They increase in length with each successive pair and overlap like the tiles of a roof from the front backward seen in ventral view, and thus the coxae of the last pair of legs are not covered. Their sides are furnished, with smooth gliding faces. In Eurypterus and Hughmilleria the fourth coxa possesses a circular perforation covered by a thin membrane and this is also present in Limulus. Holm first observed this, suggesting from its structure and position near the inner margin of the coxa which is exposed to the outside, that it was an auditory organ. This perforation is here figured in Eurypterus remipes [pl. 7, fig. 6] and Hughmilleria socialis [pl. 62, fig. 5].
Patten [1894] has indicated that the spines on the anterior portion of the gnathobase of Limulus serve as gustatory organs. The inference is proper that the thick, blunt, hollow spines observable in like position in Eurypterus fischeri [see Holm, op. cit. pl. 2, fig. 5–8] and other eurypterids [pl. 16, fig. 1] had a like function.
Figure 12 Eurypterus fischeri Eichwald. Coxa of fourth left endognathite, seen from below (outside), showing epicoxite at right and circular perforation. (From Holm)
The coxae of the second to fourth pairs of limbs of Limulus bear a small, movable appendage behind the inner end of the manducatory edge, which is also found in the scorpion. This is known as the epicoxite. It is furnished with fine bristles and small brushes and has a tactile function. Laurie discovered this articulated process in Slimonia [1893, p. 511] but was unable to determine how many and which pairs of legs bear it. Holm found epicoxites on the first to fourth pairs of the
