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. Colossendeis, 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. Nymplion 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 2 M 



