REPORT ON THE CRUSTACEA MACRURA. 



779 



joint, which terminally supports two long flagella, of which the upper and outer sends 

 off a third that is shorter than the others. 



The second pair of antennae is armed with a tooth at the outer and lower distal 

 angle of the first joint of the peduncle, carries a scaphocerite that is about two-thirds 

 the length of the carapace, and terminates in a long flagellum. 



The mandible consists of a strong molar process projecting at right angles with 

 the apophysis, and separated from a strongly dentate psalistoma, at the outer side of 

 the base of which stands a three-jointed synaphipod of considerable tenuity. 



The second pair of gnathopoda is pediform, having only three joints exposed, of 

 which the terminal is the shortest and ends in an obtuse point, and the basis carries 

 a rather slender ecphysis. 



The first pair of pereiopoda is slender and chelate, the carpos being long, slender, 

 and uniarticulate. The second pair of pereiopoda resembles the first in form, but 

 is longer and larger, and has the carpos uniarticulate. The three following pairs 

 resemble each other in form and proportions, and approach in length that of the 

 second pair ; the dactylos is uniunguiculate, the propodos long and cylindrical, and the 

 carpos has the anterior distal angle produced beyond the carpal joint of the propodos. 



The pleopoda are robust, foliaceous and biramose. 



The rhipidura has the outer branch with a diaeresis. 



The branchiae consist of seven pairs arranged as in the following table : — 



Pleurobranchiee, 

 Arthrobranchi®, 

 Podobranchise, 

 Mastigobrancbiee, 



1 

 1 

 r 

 h i 



Observations.- — This genus was first founded by Fabricius, in 1798, for those 

 species of Macrura that had "four, unequal, pedunculated antennae. The first 

 (superiores) pair the shorter, trifid, setaceous, the middle branch being the shortest 

 (lacinia intermedia breviore). The second (inferiores) antennae very long, setaceous, 

 and simple." 



In his list the following species and habitats are given : — 



Palsemon carcinus, American Eivers. 

 Palsemon lar, East India. 

 Palsemon longimanus, East India. 

 Palsemon brevimanus, East India. 

 Palsemon coromandelianus, East India. 



Palsemon tranquebaricus, East India. 

 Palsemon squilla, European Seas. 

 Palsemon locusta, Ocean. 

 Palsemon serratus, Norwegian Sea. 

 Palsemon fucorum, Ocean weed." 



Of these Palsemon carcinus, Palsemon squilla, and Palsemon locusta appear in 

 Linnaeus' Systema Naturae under the general carcinological name of " Carcinus," 



