14 CALIFORNIA ACADEMY OF SCIENCES. 



The Second Maxillipeds. — The second maxillipeds are 

 more like the third pair than the first; the endopod is 

 well developed and generally contains the typical num- 

 ber (five) of joints. The exopod is also well developed 

 and furnished with a terminal palp. The epipod often 

 bears one or more gills. 



The Third Maxillipeds. — The endopod of the third 

 maxillipeds is usually composed of five joints. In the 

 Brachyura the ischium and merus are flattened and 

 generally fitted neatly to the buccal area; the last three 

 joints are small and are termed the palp; in the 

 Macroura the joints of the third maxillipeds are usually 

 rounded. The exopod may be well developed, but is 

 sometimes vvanting. 



The Thoracic Legs, or Pereopods. — The thoracic legs, 

 with rare exceptions, consist of seven joints, two or 

 more of which are generally fused together. The exo- 

 pod is wanting, except in some of the lower Macroura, 

 where it is represented by a small, jointed appendage. 

 One or more of the thoracic legs may be furnished with 

 pincers or chelae, in which case they are called chelipeds; 

 the movable finger of the hand, or chela, is called the 

 dactyl, the immovable one the pollex; the basal portion 

 of the hand is known as the palm. 



The Abdominal Appendages, or Pleopods. — The pleo- 

 pods in the Macroura are generally furnished with 

 flattened rami adapted for swimming; the posterior pair 

 is usually much larger than the others and forms with 

 the telson a strong tail fin. In the Brachyura these 

 appendages are never employed in swimming; in the 

 females they are used for holding the ova; in the males 

 only one or two of the anterior pairs are retained as 

 sexual appendages and these are sometimes wanting. 



