gg ECHINOIDEA. II. 



and even to the Echmidm and Echhiomctridcr the>- seem to show affinities, viz. through their <large 

 headed> (tridentate) pedicellarise (Op. cil. p. 132). — In the Pananiic Deep-Sea Ech. • p. 150 Professor 

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

 outline, deeplv sunken actinal and anal grooves, its well developed anal proboscis, and such a t>pe 

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

 anchytid type, represented by Urechinus and C>stechinus. In the further development the rudimentary 

 phyllodes and labiun; become specialized in CTCuicopatagus, Argopatagus and Homolampas. Next An- 

 anchytid petals like those of Paleopneustes, I^inopneustes lead us gradualh- to the petaloid t>pe of 

 the recent Spatangoids >. — On p. 173 it is stated for Argopatagus that the fact that the second plates 

 of the posterior zone of the posterior lateral ambulacra almost separate the labium from the sternum 

 as in Plexechinus is an iudication of the affinities of the genus to the Pourtalcsiae >. 



Aeassiz thus evidentlv seems to con.sider the Pourtalesise as the centre from which all the 

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

 named does not seem to be the meaning of the famous Echinologist — the Pourtalesise 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- 

 talesise are highly specialized, not at all embryonic. 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 relationshii?. (Comp. mj- remarks on this theme in the Echinoidea of the Danish Siam- 

 Exped. p. 50.) 



Also Urechinus iiarcsianus is held by Agassiz («Blake»-Ech. p. 52) to be a representative of 

 the oldest Spatangids, -leading us little by little to Spataugoid genera in which the ambulacra become 

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

 Spatangus proper, with well defined petaloid ambulacra and a highly developed subanal fasciole etc. 

 It is evident that the (piite rudimentary al)actiual tul)e-feet and pores in Urrcliiints is a highly .speci- 

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

 pletely 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 develo])ed, should again give rise to petaloid structures with large, double pores 

 and well developed tube-feet. Also the fascioles have doubtless developed separateh- in se\-eral groups 

 — in the same manner as the i)ol\])orous condition of the ambulacra among the Echiiiiiia. — The 

 same objections may l)e made against regarding Cc//)'w;/^' as liolding an iuti.r'.nediate position between 

 the Pourtalesia; proper and such genera as Paleopneustes and Pahcotropus , and against finding in 

 Cystcchimis (Urcchimts), Pourtalesia — and the allied genera Palcrotropus, Neolampas and the like 

 a proof of <the affinities of the Spatangoids with the Echiuolampadie \ (< Chall. -Ech. p. 148). — ITpon 

 the whole I cannot join Profe.s.sor Agassiz when expressing his joy of how the structure of so many 

 of the Spatangoid forms is .satisfactorily explained by the different genera of Pourtalesise collected l)y 

 the Challenger" and how greatly the kn(nvledge of the uiL-uil)eis of this fauiih has lielj)cd us to 



