74 THE VOYAGE OF H.M.S. CHALLENGER. 



Observations. — This specimen carries a large number of ova containing embryos 

 that are far advanced in development, a circumstance that has enabled me, after much 

 trouble and care, to determine the form of the brephalos. 



The ovum is about 0"3 mm. (0'012 in.) in diameter, and is perfectly round. By the 

 aid of liquor potassae I was able to make out the form of the eyes, since they were 

 projected on long stalks. The outer or second pair of antenna? is small and cylindrical, 

 but the first or inner pair I could not determine, nor the exact form of the carapace, and 

 I am therefore doubtful whether it only covers and protects the cephalon as in the 

 brephalos of Palinurus, or overlies the pereion also, as figured by De Haau in his species 

 of Phyllosoma guerini, which has all the appearance of being a more advanced stage of a 

 young Scyllarus or Ibaccus. 



Three pairs of pereiopoda are well advanced, and carry a basecphysis or branch 

 springing from the extremity of the second or basisal joint, which is also well developed 

 in the two anterior pairs, but represented only by a small bud-like process in the 

 third. 



The pleon is short and rudimentary. The entire brephalos, when outstretched at the 

 period of extraction from the egg, was about 0"5 mm. (0'02 in.) in length, measuring from 

 the frontal margin between the eyes to the telson, and resembles the Phyllosoma 

 of Palinurus in its general appearance. 



This species was taken on the 10th of February 1873, in 78 fathoms of water, with 

 two smaller specimens that I am inclined to consider as immature forms of another 

 species, the reasons for which are given in the description of Arctus immaturus. 



The temperature of the bottom water is not recorded, no temperature sounding 

 having been taken at this station. 



*«-> 



Family Palinurida 



Carapace longitudinally sub-cylindrical, ophthalmopoda having orbits only partially 

 excavated in the cephalon, second pair of antennae terminating in a long rigid multi- 

 articulate flagellum. 



This family forms the tribe of "Langoustiens," which contains but one genus Palinurus, 

 and this Milne-Edwards has in his Histoire des Crustaces divided into two subgenera, 

 " Langoustes ordinaires," of which Palinurus vulgaris is the type, and " Langoustes 

 longicornes." This latter he again subdivides into — (l) those species which have the 

 pleon transversely furrowed, of which Palinurus guttatus is the type ; and (2) those in 

 which the pleon is not furrowed, of which Palinurus fasciatus is the type. 



More recently Dr. Camil Heller, in his volume on the Crustacea which were taken 

 during the cruise of the frigate " Novara," has, like Milne-Edwards, arranged the species 

 under one genus, which he places in two divisions, as follows — 



