KCHINOIDKA. II. 



the use (or rejection) of generic names first used for fossil tonus, since I retain the names Arbacina, 

 Porocidaris and Stereocidaris. As regards Stereocidaris, I think it quite right to maintain that name, 

 the structure of the test being so characteristic that it seems beyond doubt that the recent and fossil 

 species belong to the same genus. (Comp. Doderlein. Op. cit. p. 95.) Regarding Porocidaris, I find it 

 rather doubtful, indeed, whether it really belongs to the same genus as the fossil type, and perhaps 

 it would be better to create a new genus for it; for the present, however, I will leave that undecided. 

 It was probably wrong to accept the name Arbacina - even if the species forbesianus had not 

 proved to be a Prionechinus. On the other hand, it was probably unnecessary to revive the name 

 ( cenopedina — but upon the whole I must maintain that in those families, where the pedicellarise are of 

 great systematic importance, it is generally quite impossible to say with certainty to which genus, 

 or in several cases even to which family, a species belongs of which onlv the test is known, as is 

 generally the case with the fossil forms. To my remark on this subject (Parti, p. 85) that identical 

 structure of the test is no proof of near relationship ■ , Professor Agassiz objects (p. 107) that we are 

 perfectly justified in retorting that similarity of the pedicellarise is no proof of relationship as shown 

 by the structure of the test, and we are not warranted in classifying together forms which agree only 

 in the structure of the pedicellarise, and differ in the structure of the test . I quite agree with this 

 and have never thought of maintaining that the structural differences found in the tests of the differ- 

 ent forms were of no systematic value, and I think that Agassiz will be unable to point out any 

 case of my having associated forms differing essentially in the structure of the test on account of their 

 pedicellarise being alike in structure, except — perhaps — among the Cidarids, where ray material did 

 not allow me to study sufficiently the differences in the structure of the test. Professor Agassiz is 

 not at all entitled to say that I recognize(s| only such affinities as are indicated by the structure of the 

 pedicellarise. Affinities indicated by other structural features have little or no interest for him, or are 

 entirely erroneous. It will be a great saving hereafter if illustrations of Echini are limited, as he would 

 have us limit them, to figures of pedicellarise-. — I need again only refer to the chapter on the classi- 

 fication of the Diadematids in my work on the Siam-Echinoidea for refutation of this assertion, and as 

 regards the illustrations a mere glance at my work will show that I have figured the species treated 

 there as carefully as possible. I wish Professor Agassiz had done so with all the species described bv 

 him — that would have saved his fellow-workers a great deal of trouble; I may remind the eminent 

 author of such species as Echinus Wallisi, Dorocidaris Bartletti, Hemiaster Mentzi. On the other hand, 

 I would maintain that for a preliminary description of some species, figures of the pedicellarise may be 

 much more valuable than a figure of the whole animal, on which none of the more important char- 

 acters can be seen. And it may also be suggested that not everybody perhaps can afford the expense 

 of so copious illustration as that given in Professor Agassiz' last magnificent work. 



Against the results of my studies on the Echinothuridm Professor Agassiz has made a great 

 many objections, only very few of which, however, I can acknowledge as maintainable. I shall answer 

 them one by one in the order in which they are set forth. 



Firstly, Professor Agassiz objects to the arrangement of the figures of pedicellarise in my plates; 

 he finds it almost impossible to compare the figures of pedicellarise of the different species < without 

 a guide or key to their arrangement (p. 81). It is, indeed, rather a difficult question how to arrange 



The Injrolf-Expedition. IV. 2. ^ 



