180 



The antennas are profoundly modified : from the dorsal view each consist s 

 of a pair of large laminae which appear to represent the 3rd and 5th joints of th e 

 peduncle : there is no antennal scale and the basal joint of the peduncle is 

 merged in the epistome. 



The 2nd maxillae and 1st maxillipeds appear to take no part in mandu- 

 cation. 



All the maxillipeds have exopodites and epipodites : the external maxilli- 

 peds are pediform and six-jointed, the basis and ischium being fused. 



The thoracic legs ai*e six-jointed, the basis and ischium being fused : none 

 are enlarged and none are chelate except the 5th pair in the female which is 

 more or less perfectly so : the first four pairs carry large foliaceous epipodites. 



The 1st abdominal somite is, in both sexes, destitute of appendages. 



This family is represented in the depths of these seas by two species of the genus Arctns. 



ARCTUS, Dana. 



Aretus, Dana, Proc. Aead. Nat. Sci. Philad., 1852, p. 14, and U. S. Expl. Exp., Crnst., pt. I., p. 516: Spence 

 Bate, Challenger Crust. Macrnra, p. 66. 



Carapace depressed, shorter than the abdomen, its greatest breadth equal 

 or nearly equal to its length : the ophthalmic and antennal terga though an 

 integral part of it, are distinctly recognizable : its posterior angles are firmly 

 held between a stud-like facet of the last thoracic epimeron below, and the 

 incurved angle of the rudimentary 1st abdominal pleuron above. 



Eyes of good size, orbits dorsal and situated nearer to the antero-lateral 

 angle of the carapace than to the middle line. Antennular flagella extremely 

 short. Antennas not in contact with one another. 



The mandible carries a short setose palp and has no separate molar process. 

 The 1st maxillae consist of a slender curved coxopodite and basipodite, without 

 palp. The 2nd maxillae consist of an enormous scaphognathite with the other 

 parts rudimentary. In the 1st maxillipeds the coxopodite is absent, the basipod- 

 ite and endopodite small, and the epipodite and exopodite large and foliaceous, 

 the exopodite forming a sort of tongue-like valve in the efferent branchial 

 channel. In the 2nd maxillipeds the exopodite is foliaceous and much larger 

 than the endopodite and projects at the efferent branchial opening : the endopod- 

 ite is pediform and six-jointed, and a slender epipodite is present. The ex- 

 ternal maxillipeds are pediform and six-jointed : their exopodite is slender and 

 has no flagellum. 



The 1st abdominal somite is destitute of appendages, the 2nd has them 

 well developed in both sexes, while on the 3rd-5th somites they are present in 

 the female but are sometimes rudimentary or absent in the male. 



