146 A HISTOEY OF EECENT CEUSTACEA 



CHAPTER XT 



SUB-ORDER II. — MACRURA 



The carapace in general is shorter than the pleon and has 

 the ' front ' produced into a more or less decided rostrum. 

 The stalked eyes are not enclosed in orbits, but usually 

 rest in a hollow on the upper surface of the basal joint of 

 the first antennae. Both pairs of antenna are generally 

 elongate, the first not planted in fossettes, the second 

 usually carrying a scale or acicle attached to the second 

 joint. The third maxillipeds are elongated and pediform. 

 The five pairs of perasopods or limbs of the trunk vary 

 greatly, as any of them may be chelate and any of them 

 simple. The sternal plastron or breastplate is linear in 

 general. The vulvae of the female open in the basal joints 

 of the third pair of legs, and the vasa deferentia of the 

 male pass through those of the fifth pair. The pleon is 

 seldom completely reflexed against the breastplate. Of 

 the six pairs of pleopods the first varies from the succeed- 

 ing, and all may be absent ; but except in the Lithodidae 

 that belonging to the sixth segment is always present, 

 this pair with the telson forming the Bhipidura or tail-fan. 

 Otoliths of some kind are very commonly present in the 

 basal joint of the first antennj^. 



In the above definition the Pterygurous division of 

 Milne-Edwards' Anomura is included. After explaining 

 the grounds upon which Milne-Edwards had introduced 

 his tripartite arrangement, de Haan makes the following 

 comment upon it : — ' The division of the Decapoda into 

 Brachyura and Macroura is for various reasons to be pre- 



