ECHINOIDEA. II. 



and even to the Echinidcr and Echi>ioiiietndæ they seeni to show affinities, viz. through their large 

 headed: (tridentate) pedicellariæ (Op. cit. p. 132). — In the Panamic Deep-Sea Ech.> p. 150 Professor 

 Agassiz finds it interesting to trace the changes between Pourtalesia proper with its bottle-shaped 

 outHne, deeph- sunken actinal and anal grooves, its well deveioped anal proboscis, and such a t>pe 

 as Plexechinus, in which the Pourtalesian features have almost disappeared, to pass into a more An- 

 anchytid t>pe, represented by Urechinus and Cystechinus. In the fnrther developnient the rudimentary 

 phyllodes and labiuni become specialized in Genicopatagus, Argopatagus and Homolampas. Next An- 

 anchytid petals like those of Paleopneustes, Linopneustes lead ns gradually to the petaloid type of 

 the recent Sjrntangoids >. — On p. 173 it is stated for Argopatagus that the faet that the second piates 

 of the posterior zone of the posterior lateral ambulacra almost separate the labinm from the stem nm 

 as in Plexechinus is an indication of the affinities of the genus to the Pourtalesiæ >. 



Agassiz thus evidently seems to consider the Pourtalesiæ as the centre from which all the 

 other Irregular Echinoids have deveioped; that the group itself has deveioped from one of those 

 named does not seem to be the meaning of the famous Echinologist — the Pourtalesiæ are evidently 

 regarded as «embryonic» forms, which have given rise to all the different groups, to which the affi- 

 nities are pointed out, since the affinities probably must mean real genetic relationship. I think I 

 need not here point out in a more detailed manner that the more prominent characters of the Pour- 

 talesiæ are highly specialized, not at all embryouic. But Professor Agassiz does not seem to take 

 into consideration that the different characters are not of the same value; structural characters of 

 the highest systematic importance and irrelevant, vague resemblances are regarded as equivalent 

 criteria of relationship. (Comp. my remarks on this theme in the Echinoidea of the Danish Siam- 

 Exped. p. 50.) 



Also Urcchmus narcsiauus is held by Agassiz ( Blake -Ech. p. 52) to be a representative of 

 the oldest Spatangids, leading us little b\- little to Spatangoid genera in which the ambulacra become 

 more or less petaloid, as in Homolampas, Paleopneustes and the like, till we get the modern type of 

 Spatangus proper, with well defined petaloid ambulacra and a highh- deveioped subanal fasciole etc. 

 It is evident that the quite rudimentary abactinal tube-feet and pores in Urechinus is a highly speci- 

 alized feature, which may possibly give rise to further stages in which thcse tube-feet and pores com- 

 pletel)- disappear; but it is rather inconceivable how these rudimentary pores and tube-feet, which 

 doubtless represent a reduction from the more primitive condition, where the pores were double and 

 the tube-feet well deveioped, should again give rise to petaloid strvictures with large, double j^ores 

 and well deveioped tube-feet. Also the fascioles have doubtless deveioped separately in several groups 

 — in the same manner as the polyporous condition of the ambulacra among the Echinina. — The 

 same objections may be made against regarding Calyiiinr as holding < an intermediate position between 

 the Pourtalesiæ proper and such genera as Paleopneustes and Palæotropus , and against finding in 

 Cystcchimis ( Urcchimts), Pourtalesia — and the allied genera Pala-otropus, Neolampas and the like» 

 a proof of ' the affinities of the Spatangoids with the Echiuolampadæ*. («Chall. -Ech. p. 148). — Upon 

 the whole I camiot join Professor Agassiz when expressing his jo\- of how the structure of so many 

 of the Spatangoid forms is satisfactorily explained by the different genera of Pourtalesiæ collected by 

 the Challenger» and how greath- the knowledge of the members of this famil\- has helped us to 



