Mr. L. J. Colo on Ten-legged PgcnogoniJs. 411 



names derived from their most specialized forms ; for one I 

 have therefore used the name Pvcnogonomorpha, Pocock, 

 given by Laukester (19C4, p. 225), while for the sake of 

 consistcney I have proposed the term Colossendeomorpha 

 for tlie other order. 



In Decolopoda, of all known Pycnogonids, we have the 

 most primitive conditions. Here the chclifori are avcU 

 developed and strongly chelate, the palpi are present and 

 made np of ten joints, the ovigeraare present in both sexes * 

 and are provided with denticulate spines, and the trunk- 

 segmentation is distinct. In the Pycnogouomorpha we find 

 that there is a gradual tendency to a redaction of the ante- 

 rior appendages : the chelifori are lost in the Phoxichilidje ; 

 in the palpi the joints are reduced one half in number at the 

 beginning, and are lost entirely in some of the Pallenidae ; 

 the females no longer bear ovigera in the Plioxifhilidiidte, 

 and in Hannonia the denticnlate spines are lacking from 

 these appendages; the segmentation remains distinct and 

 well marked throughout. In the Colossendeomorpha the 

 chelifori have rather rudimentary chelae in the Eurycydidte, 

 are present (usually) but not chelate in adult Ammotheidaj, 

 and are lost entirely in the Pasithoidaj; the palpi remain 

 well developed throughout, but ai*e reduced as to tie number 

 of joints composing them in the Ammotheithe, in which 

 character they make a slight break in the gradation of the 

 series t ; the ovigera are retained in both sexes throughout, 

 though the denticulate spines are lost in the Pasitlioidaj ; 

 the trunk-segmentation shows a direct gradation from a 

 well-marked condition in the Eurycydidae to a complete 

 coalition in the Pasithoidae, both conditions bL'ing fouud in 

 the intermediate family. 



The most remarkable features in these two series are the 

 directness of the two lines of difi'erentiation and the similar 

 tendency in both to a reduction of the parts. Each of the 

 families is intermediate, in the characters commonly used for 

 their distinction, between the one that precedes and the one 

 that follows (with the minor exception in the case of the 

 Ammotheidae, as noted). This approaches the kind of 

 " chain " that was looked for by some of the early evolu- 



• "Of the many specimens that I obtained I saw none but such as 

 were furnished with what are termed the egg-bearinu; organs, conse- 

 quently if those are the females that are thus distinguished, they prove 

 much mure numerous than the males." — Eights (1837, p. 205). It is 

 probable that he had both sexes. 



+ This is indicated in the diagram by representing the Ammotheidae 

 as having branched ofl' slightly from the direct line. 



28* 



