SEARCHING- BRANCHLE 213 



CHAPTER XVI 



TRIBE VI. PEX^IDEA 



THE branchial structure typically consists of a series of 

 plumes, that are attached by, or very near, their basal 

 extremity to the animal, and from a long- central stalk 

 send off on each side a single row of branches that divide 

 and subdivide in a variety of ways according to the genus 

 or even the species. The appendages of the trunk are 

 supplied with nerves from separate ganglionic centres, 

 except the last pair, which is supplied not from its own 

 segment but the preceding. The third pair of trunk-legs 

 are chelate, the two following pairs never are. The ex- 

 truded ova do not appear to be definitely attached to the 

 appendages of the mother prior to hatching as in most 

 other Macrura. The first larval form is supposed to be a 

 Nauplius. 



This tribe corresponds with what Spence Bate calls 

 the Dendrobranchiata normalia, in allusion to the rami- 

 fied, or tree-like structure of the branchiae. He allots to 

 it two families, the Penasidas and Sergestidas. 



Family 1. Penceidce. 



The carapace at the sides is deeply produced and 

 carried further back than in the median dorsal line ; its 

 rostrum is laterally compressed, this part at least being 

 carinated. Of the segments of the pleon the first three 

 are usually not longitudinally carinate, but the three that 

 follow are almost always much so. The sides of the first 

 are produced so as to overlap the hind lateral margin of 

 the carapace and the front lateral margin of the second 



