Sub-Glass 1. Entomostracco- Order 2. Gladocera. 



197 



compound sessile eyes ; the naupliuseye is represented by a 

 pair of ocelli, placed near together. Antennae and jaws are 

 entirely wanting. Ventrally there are six pairs of jointed 

 ambulatory limbs, all of which are, in the female, furnished 

 with chelffi (c/. Decapoda), whilst in the male these are frequently 

 wanting from some of the limbs. 



The six pairs of walking legs surround the mouth, which is iasf 

 back; the first pair, which is much smaller than the others, is 

 in front of the mouth; the basal joints are beset with spines, so 

 as to serve also as masticatory organs. On the ventral side of the 

 abdomen there are five pairs of lamellate limbs; the members 

 of a pair are concrescent at the bases of their inner edges ; and each 

 limb bears on its posterior side a number of broad, low, branchial 

 1 a m e 1 1 88 . From the hinder edge of the cephalo-thorax arises a 

 pair of similar lamellate but more chitinised and gill-less appendages, 

 which coalesce in the middle-line, and cover the gill-bearing limbs as 

 an operculum. On the posterior side of the operculum, in 

 both male and female, are the two genital apertures. The body 

 terminates in a long, movably-jointed, pointed caudal-spine. 

 The exoskeleton is tolerably hard, of a horny consistence and 

 colour. 



The young Limulus hatches at a comparatively advanced stage. 

 When newly-hatched it is peculiar in having a jointed abdomen 

 and slightly developed caudal-spine. 



Fij. 158. Young Limulus. A dorsal, B ventral. — After Kingsley. 



The few extant species of this group are large (to over '5 m. long), 

 and come from the coasts of Asia and America. The caudal-spiue 

 plays a not unimportant part in locomotion, for it is used to push the 

 body forwards. The Xiphosura are carnivorous. 



Some of the extinct forms exhibit a segmented abdomen like that 

 of the young Limulus [i^.g. Belinurus, from the Carboniferous). More 



