210 



MANUAL OF ZOOLOGY. 



articulated to the dorsal buckler, and giving the name to the 

 sub-order. 



The chief features, therefore, which characterise the Limulus 

 are as follows : i. The possession of six pairs of appendages 

 which are placed round the mouth, have their bases spinous, 

 act as jaws, and have their free extremities developed into 

 claws; 2. The possession of six abdominal pairs of appendages, 

 expanded for swimming, and carrying the gills ; 3. The posses- 

 sion of a semicircular buckler, covering the cephalothorax, and 



Fig. 66. Xiphosura. Limulus polypke- 

 mus, viewed from below, c The cephalic 

 shield carrying the sessile eyes upon its 

 upper surface ; o "Operculum," covering 

 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 

 t>y Woodward as being respectively, from 

 before backwards, the great antennae, the 

 mandibles, the first maxillae, the second 

 maxillae, and a pair of maxillipedes. All 

 have their extremities chelate. 



Fig. 67. Eurypterida. Pterygotus An- 

 glicus, restored (after H. Woodward). 

 c c Chelate antennae ; o o Eyes, situated 

 at the anterior margin of the carapace ; 

 m m The mandibles, and first and se- 

 cond maxillae ; n n The maxillipedes ; 

 the basal margins of these are serrated, 

 and are drawn as if seen through the me- 

 tastoma 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 (f). 



carrying the eyes upon its upper surface; 4. The possession 

 of a second buckler, or " operculum," covering the abdomen ; 



