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 ischiurn 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 wanting. 



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 chelte, 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. 



