XXI CLASSIFICATION 529 
The classification here adopted is a compromise between a 
natural system, so far as we can detect it, and an artificial 
one. 
Two forms, separated from one another by many differences, 
show a minimum of degeneration, namely Decolopoda on the one 
hand, and the Nymphonidae on the other. The former genus 
has five pairs of legs, and this peculiarity is shared by Penta- 
nymphon. In both groups the three anterior limbs are all 
present and well formed, save only that the ovigerous legs, which 
have ten joints in Decolopoda, are reduced to five joints in the 
Nymphons, and their denticulate spines, of which several rows 
are present in the former, are reduced to one row in the latter ; 
on the other hand, a greater or a less degeneration of these limbs 
marks each and all of the other families. 
Decolopoda is very probably the most primitive form known, 
though it has characters which seem to be the reverse of 
primitive in the dwarfish size of its chelophores and the crowded 
coalescent segmentation of the trunk.  OColossendeis, in spite of 
its vanished chelophores, is probably closely allied: the shape 
and segmentation of the body and the several rows of smooth 
denticles on the ovigerous legs are points in common. The 
Eurycydidae are closely allied to Colossendeidae; they agree 
with Decolopoda in the two-jointed scape of the chelophore, and 
with Ammotheidae in the deflexed mobile proboscis. The true 
position of Rhynchothorax is very doubtful. 
The Nymphonidae and Pallenidae are closely allied, and the 
Phoxichilidiidae have points of resemblance, especially with the 
latter. Mymphon compares with Decolopoda in the completeness 
of its parts, and is more typical in its long well-segmented body, 
and in its highly-developed chelae; but it already shows reduc- 
tion in the scape of the chelophore, in the palps, and in the 
armature of the ovigerous legs. 
The Phoxichilidae and Pycnogonidae (Agnathonia, Leach ; 
Achelata, Sars), though differing greatly in aspect, are not im- 
probably allied to one another; and whether this be so or not, the 
complete absence of chelophores and of palps affords an arbitrary 
character by which they are conveniently separated from all the 
rest. 
The following table epitomises the chief characters of the 
several families :— 
VOL. IV 2M 
