A REVISION OF THE BRITISH IDOTEID^E. 731 



consisting of a single clavate joint. On the dorsal surface of this joint are a varying 

 number of groups of sensory setae, probably of an olfactory nature. 



3. Antennas. — There are five peduncular joints in these appendages, and usually 

 a multiarticulate fiagellum. In Erichsonella, Benedict, Eusymmerus, Richardson, 

 Zenobiana, Stebbing, and Symmius, Richardson, the joints are united to form a single 

 piece. In Edotia, Guerin-Meneville, the antennae are rudimentary, and the fiagellum 

 consists of a single joint. Terminally there is a more or less conical style with a 

 number of long fine setae at the apex. 



4. Oral Appendages. — These include the upper and lower lips, the mandibles, 

 the first and second maxillae, and the maxillipedes. The lips have been regarded by 

 most authors as integumentary modifications rather than true appendages, although 

 Miss Arms " maintains that the leaves of the lower lip ' are independent outgrowths 

 or buds from the integument, as much as any other pair of appendages ; and the fact 

 that the parts of the segment to which they must have belonged have disappeared, 

 or cannot be readily found is,' in her opinion, ' an argument of doubtful weight ' " (66). 

 The upper lip is plate-like, and projects from the dorsal border of the mouth over the 

 mandibles ; a second and inner plate is present in some Isopoda. The lower lip is 

 bilobed, and consists of a small inner pair of lobes and an outer larger pair. 



The mandibles are without palps ; each consists of a stout robust body with a 

 bidenticulated apical portion, below which is a broad truncated molar tubercle. 

 There is considerable variation in the form of the teeth, according to age, etc. 



The first maxillae each consist of a short robust outer lobe terminating in a 

 variable number of stout curved spines, and an inner series of more slender ones, 

 which may be simple or toothed. The inner lobe is a thin, flat, narrow chitinous 

 band with a series of, usually setose, spines terminally. In Idotea, Fabricius, Mes- 

 idotea, Richardson, Glyptidotea, Stebbing, Zenobiana, Stebbing, Paridotea, Stebbing, 

 Pentias, Richardson, and Synisoma, Collinge, there are three of these spines ; in 

 Synidotea, Harger, and Engidotea, Barnard, only two.* 



The second maxillae each arise from the protopodite as two flat laminar lobes, the 

 innermost of which is bilobed ; all of them are fringed with long setae. 



The maxillipedes each consist of a coxopodite which is divided into two, a basal 

 segment or basiopodite composed of a single joint ; articulating with this distally is 

 the palp or endopodite, on the outer side is an epipodite, whilst on the inner side is 

 a short joint articulating with the basal segment, which joint is provided with one or 

 more peculiar handle-shaped appendages known as the coupling processes. 



In CJiiridotea, Harger, Synidotea, Harger, Edotia, Guerin-Men., Chiriscus, 

 Richardson, Symmius, Richardson, and Macrochiridothea, Ohlin, the palp is three- 

 jointed ; in Idotea, Fabricius, Colidotea, Richardson, Eusymmerus, Richardson, 

 and Erichsonella, Benedict, four-jointed ; in Mesidotea, Richardson, Pentidotea, 



* In an Australian form (genera unci species as yet undetermined) there are four spines present. Paridotea ungu- 

 lata also has four. 



