ANNULOSA: CRUSTACEA. 



301 



Trilobites, such as Trinucleus and Asaphus. After hatching, 

 the previously existing segmentation is soon obliterated, and, 

 three or four weeks later, the telson assumes the ensifonn 



Fig. 150. Xiphosura. Limulus 

 mus, viewed from below. c The ce- 

 phalic shield carrying the sessile eyes 

 upon^ its upper surface; o " Opercu- 

 lum," covering the reproductive organs ; 

 b Branchial plates ; a First pair of an- 

 tennae (antennules) ending in chelae. 

 Below these is the aperture of the mouth, 

 surrounded by the spiny bases of the re- 

 maining five pairs of appendages, which 

 are regarded by Woodward as being re- 

 spectively, from before backwards, the 

 great antennae, .the mandibles, the first 

 maxillae, the second maxillae, and a pair 

 of maxillipedes. All have their extremi- 

 ties ch elate. 'j;." 



polyphe- Fig. 151. Eurypterida. Pterygotus An- 

 The ce- 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 the first and 

 second maxillae ; nn 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 (t). 



shape characteristic of the adult. According to the views of 

 Van Beneden, the development of Limulus so closely resem- 

 bles that of the Scorpions, that the former should properly be 

 removed from the Crustacea, and placed in the Arachnida. 



The King-crabs are found in the Indian and Japanese seas, 

 on the coasts of North America, and in the Antilles. They 

 sometimes attain a large size, and both the eggs and the flesh 

 are eaten by the Malays. 



SUB-ORDER 2. EURYPTERIDA. " Crustacea with numerous, 



