TEEEESTEIAL KSOl'ODA OP NEW ZEALAND. 103 



he liemis. In Ligia the dactylar seta is luiln-cxnched aud slightly cluhhed at the end ; in 

 TricIioniscK.s it divides into two brandies, each further subdividing into line filaments ; 

 in S'ci/p/ioiiiscKS it divides similarly, though differing a little in detail ; in 2)/Ion it 

 is rather short, unbranched, and has the distal iialf thicker and stippled-looking ; in 

 Actiecia cuchroa it is somewhat similar ; while in Acta-cia (?) uplheus'ts it is larger and 

 very distinct, and the stippled appearance of the distal portion looks under a high power 

 as if it were caused by the distal portion, resembling a narrow circular brush with short 

 hairs projecting all round it. It is sometimes lost in specially old aud large specimens, 

 but with this exception is always to be found in the genera mentioned ; I cannot, 

 however, find it at all in ScypJiax, Oiiiscm, Phlloscla, Armadillidinm, and Armaditlo. 

 Beyond the suggestion that it is a tactile organ, I can give no iiiformation as to its 

 function. A seta, probably aLso of a sensory nature, is found similarly situated in 

 Asellus aquaticm and some other Isopods, and also in many Amphipods, but in these it 

 is less prominent, and does not take such A'aried forms. 



In all the genera, and especially those Jiitherto imperfectly known, I have examined 

 the mouth-organs in some detail ; an accurate knowledge of these will, I think, in time 

 help us on to\vards a natural classitication of this group, for they seem to be much more 

 constant than characters taken from the general shape of the body, from the uropoda, or 

 even from the presence or absence of air-cavities in the pleopoda. It is true that we 

 may get sudden variations in some of the mouth-parts, such as that I have described in 

 the outer lobe of the first maxilla of Sci/phoniscus, or by Dollf us hi the inner lobe of the 

 same maxilla in 3IcsarmmliIlo ; but these, occurring as they do in groups in which the 

 mouth-parts are otherwise very constant, are probably to be looked upon as sudden 

 variations or " sports " that have comj)aratively little value from a classificatory point of 

 view. 



I give here a Table, based mainly on the mouth-parts, showing briefly what appear 

 to be the more important characters of the various families : — 



A. ^landibles witli well-developed molar tubercle; inner lobe of 1st maxilla with 



three plumose bristles. 



I. Uropoda not concealed nnder pleon. 



a. Antenuffi with flagellum multiartieulate; eyes large; male organ double . . Ligiid.e. 

 /;. Antcnnie with flagellum not more than G-jointed ; eyes small ; male organ 



single Tkicho.viscid.e. 



II. Uropoda concealed under pleon. 



a. Segments of pleon separate Tylid.e. 



b. First five segments of pleon coalesced Helleiud.k. 



B. Mandibles without distinct molar tubercle, its place being taken by a brush-like 



group of setae ; inner lobe of first maxilla with only two plumose bristles. 

 I. Maxillipcdes with terminal joints of moderate size ; lamellar longer than 



masticatory lobe ScvpnyEiD^. 



II. Maxillipcdes with terminal joints small aud almost rudimentary, hardly longer 

 than masticatory lobe. 

 a, Uropoda more or less projecting ; animals not rolling into perfect ball . . Omscid.e. 



