240 



MANUAL OF ZOOLOGY. 



SUB-ORDER i. XIPHOSURA. " Crustacea having the anterior 

 segments welded together to form a broad convex buckler, 

 upon the dorsal surface of which are placed the compound 

 eyes and ocelli ; the former sub-centrally, the latter in the 

 centre in front. The mouth is furnished with a small labrum, 

 a rudimentary metastoma and six pairs of appendages. Pos- 

 terior segments of the body more or less free, and bearing 

 upon their ventral surfaces a series of broad lamellar appen- 

 dages ; the telson, or terminal segment, ensiform " (Henry 

 Woodward). 



Fig. 90. Xiphosura. Lhmilus polyphe- 

 mus, viewed from below, c The cephalic 

 shield carrying the sessile eyes upon its 

 upper surface ; o " Operculum," cover- 

 ing the reproductive organs ; b Branchial 

 plates ; a First pair of antennae (anten- 

 nules) ending in chelae. Below these is 

 the aperture of the mouth, surrounded 

 by the spiny bases of the remaining five 

 pairs of appendages, which are regarded 

 by Woodward asbeing respectively, from 

 before backwards, the great antennas, the 

 mandibles, the first maxillae, the second 

 maxillae, and a pair of maxillipedes. All 

 have their extremities chelate. 



Fig. 91. Eurypterida. Pterygotus An- 

 glicus, restored (after H. Woodward). 

 c c Chelate antennae ; o o Eyes, situated 

 at the anterior margin of the carapace ; 

 in m The mandibles, the first and second 

 maxillse ; n n The maxillipedes ; the 

 basal margins of these are serrated, and 

 are drawn as if seen through the metas- 

 toma or post-oral plate, which serves as 

 a lower lip. Immediately behind this 

 is seen the operculum. or thoracic plate 

 which covers the two anterior thoracic 

 somites. Behind this are five thoracic 

 and five abdominal somites, and lastly 

 there is the telson (). 



The Xiphosura include no other recent forms than the 

 Limuli (King Crabs, or Horse-shoe Crabs) (fig. 90). They 



