Spiders and Their Near Relatives 



of insects that it is not necessary to dwell on this class 

 here. 



V. Class Pal^eostracha (Pa-lae-os'tra-cha). — This class 

 is composed almost entirely of extinct forms, there being living 

 representatives of only a single order, the Xipbosura (Xiph-os-u'ra). 

 And this order is nearly extinct; for of it there remains only the 

 genus Limulus (Lim'u-lus), represented by only five known 

 species. 



The members of this genus are known as king-crabs or 

 horseshoe-crabs; the former name is 

 suggested by the great size of some 

 of the species, the latter, by the 

 shape of the cephalothorax (Fig. 9). 



The king-crabs are marine; 

 they are found on our Atlantic 

 Coast from Maine to Florida, in the 

 West Indies, and on the eastern 

 shores of Asia. They are found in 

 from two to six fathoms of water 

 on sandy and muddy shores; they 

 burrow a short distance in the sand 

 or mud and feed chiefly on worms. 

 The single species of our coast is 

 Limulus polyphenols. 



In Limulus the body-segments 

 are grouped in two regions, cephalo- 

 thorax and abdomen ; the abdomen 

 is terminated by a long, strong 

 spine. The cephalothorax bears six 

 pairs of appendages; these correspond to the six pairs of append- 

 ages of Arachnida described later; and, as in the Arachhida, 

 none of the appendages are jaw-like. The food is crushed by 

 the basal part of the leg-like appendages, which are situated 

 round the mouth. The abdomen also bears six pairs of append- 

 ages; these are plate-like and the members of each pair are 

 united at the base. 



The first pair of abdominal appendages form a nearly semi- 

 circular plate, which nearly covers the following appendages. On 

 the posterior side of this plate are two openings, the outlets of 

 the reproductive organs. Each of the following pairs of append- 



Fig. 9. A HORSESHOE-CRAB 



(Limulus) (after Leuckart) 



