22 ECHINOIDEA. II. 



including the last mentioned species Phormosoma rigidum, the Ph. astcrias was necessarily the last of 

 them — I did not sav the last named . That the characters on which the genus Kamptosoma was 

 founded appear to Professor Agassiz <most trivial , is, of course, a matter of slight importance, since 

 he accepts the genus. In my opinion the structure of the ambulacra in this genus (which character is 

 mentioned in the diagnosis besides the characters of spines and pedicellarise) is a highly interesting 

 feature, and even Professor Agassiz himself later on in the description of Kamptosoma indistinctum 

 does not evidently think this feature so very trivial. — As regards the species indistinctum, it is to 

 be regretted that Professor Agassiz does not say a word about the characters by which it is disting- 

 uished from the species astcrias. On p. 177 (Part I) I stated that after a renewed examination of the 

 specimens from St. 272 I thought it unjustifiable to separate them from K. astcrias as a new species; 

 it might not have been cpiite inappropriate therefore to point out the characters on which the new 

 species was established. Until these specific characters are made known I must regard K. indistinctum 

 as synonymous with K. astcrias. 



To enter on a renewed discussion of the genus Hygrosoma and its delimitation from Phormo- 

 soma, on account of Professor Agassiz' remarks on that subject (p. 85 — 86), I deem unnecessary, since 

 Professor Doderlein has accepted my view thereon and given most careful and elaborate descriptions 

 of both genera, to which I may simply refer. (Op. cit p. 125, 136.) 



After describing the changes in the apical system due to age in Phormosoma liispidum Professor 

 Agassiz says (p. 95): It is this extraordinary change in the anal system which I had observed in 

 the abactinal parts of the test, which has prompted Dr. Mortensen to credit me with the most extra- 

 ordinary ignorance of the rudimentary embryological data, many of which I was the first to discover. 

 That this remarkable intercalation exists there is not the least doubt, and it naturally suggests in old 

 specimens a flow of the anal plates into the interambulacrum, similar to the flow of the ambulacral 

 plates of the corona into the buccal plates of the actinal system-. -- I must answer to this statement 

 that I have not at all credited Professor Agassiz with any ignorance of embryological facts, but only 

 criticised his statements in the Blake -Eehinoidea (p. 32) on the development of the young Phormosoma 

 placenta, and I certainly think my criticism completely justified (Part I. p. 174 — 175). Professor Agassiz 

 himself now agrees (p. 96) that his statement there of the formation of the buccal plates was erroneous, 

 viz. that they are separated from the coronal plates, and are developed, as I (Agassiz) have shown 

 in the same manner as the imbricating plates of the Cidaridse, independently of the coronal plates; 

 new plates forming on the distal surface of the actinostome, which are intercalated between the old 

 plates and the coronal plates ». That Professor Agassiz has himself found out, before my criticism 

 had appeared, that this was a mistake, does not make this part of my criticism unjustified. I might 

 have added that the conclusion necessarily derived from the statement quoted, that in the Cidaridse 

 also the buccal plates should originate in this way, is not less erroneous, as Professor Agassiz will 

 certainly also agree. 



Concerning the formation of the interambulacral plates, Professor Agassiz continues with the 

 following statement (loc. cit): On the abactinal system, on the contrary, while the plates of the genital 

 ring are well defined and seem to be distinctly separated from the coronal plates, yet new interam- 

 bulacral plates are not added independently, as in the ambulacral system, and as in the interambulacral 

 system of other young Echinoids where the genital ring remains permanently closed. The new inter- 



