22 ECHINOIDEA. II. 



including the last mentioned species P/iormosoma rigiduvi, the Ph. asterias was necessarily the last of 

 them — I did not say the «last named». Tliat the characters oii which the genus Kamptosovia was 

 founded appear to Professor Agassiz <most trivials, 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 pedicellariæ) is a highly interesting 

 feature, and even Professor Agassiz himself later on in the description of Kaviptosoma indistinchnn 

 does not evidently think this feature so xery trivial. — As regards the species indisfinctum, 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 asterias. On p. 177 (Part I) I stated tliat after a renewed examination of the 

 specimens from vSt. 272 I thought it uujustifiable to separate them from K. asterias as a new species; 

 it might not have been quite 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. iiidistiiictuiii 

 as synonymous with K. asterias. 



To enter on a renewed discussion of the genus Hygrosoiiia and its delimitation from Phoriiio- 

 soiini., on account of Professor Agassiz' remarks on that snbject (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 1 may simph- refer. (Op. cit p. 125, 136.) 



After describing the changes in the apical system due to age in Pliorviosoma Iiispiduin 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 embryologicai 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 piates into the interambulacrum, similar to the flow of the ambulacral 

 piates of the corona into the buccal piates 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 5 Blake -Echinoidea (p. 32) ou the development of the young Phormosoma 

 placenta, and I certainly think my criticisra completelyjustified (Part I. p. 174— 175). Professor Agassiz 

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

 viz. that they are <separated from the coronal piates, and are developed, as I (iVgassiz) have shown 

 in the same mauuer as the imbricating piates of the Cidaridæ, independently of the coronal piates; 

 new piates forming ou the distal surface of the actiuostome, which are iutercalated between the old 

 piates and the coronal piates . 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 uujustified. I might 

 have added that the conclu.sion necessarily derived from the statement quoted, that in the Cidaridæ 

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

 certainly also agree. 



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

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

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

 bulacral piates are not added independently, as in the ambidacral S3'stem, and as in the interambulacral 

 system of other 3oung Echinoids where the genital ring remaius permauently closed. The new iuter- 



