412 Mr. L. J. Cole on Ten-legged Pycnogonids. 



tionists, and I know of no other group where it is so direct 

 and complete. The genera within the families will un- 

 doubtedly >how much secondary branching from this direct 

 line of descent. 



While it is difficult to understand why so many characters 

 should vary in common if such were the case, still it is 

 possible that the utilization of these characters does not give 

 us a true classification. This is suggested by the positions of 

 the genital openings, as shown in the above table, as well as 

 by the structure of the ovaries and possibly some of the 

 other organs. The condition of the ovary in Nymphon has 

 led Hoek (1881, p. 131) to remark: — "1 perfectly believe, 

 however, that the occurrence of a part of the ovary in the 

 body of a Pycnogonid is rather rare, because, as a rule, only 

 the lateral excrescences remain. No doubt this must be 

 considered as a secondary condition ; and seeing that, so far 

 as I could ascertain, it is the rule in all the species of 

 Nymphon, my original opinion, that the genus Nymphon, of 

 all the genera of Pycnogonida, resembled most the hypo- 

 thetical ancestors of our group, was .-everely shaken.'"* 



The system here brought out differs in many respects from 

 that of Hoek (1881 a, p. 495), but it is interesting to note 

 how closely the form Decolopoda agrees with his hypothetical 

 genus Archipycnogonum, Avhich he postulates as follows 

 (/. c. p. 494') : — " Archipycnogonum (genre hypothetique). — 

 Pyenogoniiles de grandes dimensions, aux mandibules fortes 

 de trois articles et armees d'une pince termiualc, aux pal pes 

 longues de dix articles, aux pattes oviferes, egalement de dix 

 articles, dont les quatre derniers sont pourvus de plusieurs 

 rangees d'epines en forme de feuilles, Les pattes thoracique 

 ont huit articles et se terminent par une griffe accompagnee 

 de deux grift'es accessoires.'' Eights's description of Decolo- 

 poda agrees in all pai-ticulars with this except that he does 

 not mention the '' accessory claws,'' which, however, it is 

 fair to assume w'cre present. Hodgson mentions and figures 

 them in Pentanymphon. Had Hoek but been aware of it 

 there was no need for him to construct a hypothetical genus 

 as the starting-point of the Pycnogonids — it had already been 

 described just as he wanted it (except that it had one more 

 pair of legs than he supj)()sed) more than forty years earlier. 



Pentanymphon 1 hive placed between Decolopoda and the 

 Nympliouulie ; but Boreonymphon and Chu'tonyniphon, with 

 their compact bodies and closely approximated lateral pro- 

 cesses, would much more nearly resemble Decolopoda in 

 general appearance if they had but the fifth pair of legs. It 

 would be expected that such a character as the possession 



