280 ORDER XYPHOSURA; LIMULUS OR KING-CRAB. 



the same Sub-Class, with any of them. The Limuli, which are 

 Crustacea of considerable size, sometimes attaining the length of 

 two feet, have their bodies divided into two parts ; of which 

 the anterior, covered by a large semicircular shield (0, Fig. 506), 

 bears the eyes, the antennae, and six pairs of legs, which sur- 

 round the mouth (5), and are used both for walking and for 



FIG. 505 LIMULUS. 



FIG. 506. UNDER SURFACE OF LIMULUS. 



mastication ; whilst the posterior portion of the body, which is 

 covered by another shield of a somewhat triangular shape, 

 bears on its under surface five pairs of swimming legs, of 

 which the last is furnished with gills ; and this triangular shield 

 terminates in a long pointed process (</). Now when we com- 

 pare the appendages to the head and body of these animals, with 

 those of ordinary Crustacea, it is evident that the first pair of 

 the legs surrounding the mouth of the Limulus represents their 

 mandibles; that the second and third pairs represent their 

 maxillae ; the three following pairs of legs their feet-jaws ; and 

 the five pairs of swimming-members, abdominal fin-feet, the 

 true thoracic legs being altogether absent. Besides the pair of 

 compound eyes, characteristic of the Crustacea in general, the 

 Limuli have a pair of small simple eyes, placed anteriorly, near 



