14 ECHINOIDEA. II. 



o 



classificatory value, naturalh- led ine to suppose that the same woiild g^eiieralh be tlie case in all 

 Echinoidea. Later studies on other families of the Echinoids {Diadcmatidce , Tevinopleiiridæ . the Irregu- 

 lar Echini) ha\e showii that these structnres are not always of so high a valne in classification, and in 

 such groups the possibilitx of determination and classification of the fossil forms is, of conrse, more 

 favourable than in those gronps, where the pedicellariæ are of more importance, as in Echinidæ. Toxo- 

 pneustidæ, Ecliiiioiiiefridæ and, parth, Cidarida-. In these groups it is certainly not too much to sa\- 

 that there cannot be any great certaiuty in the classification of the fossil forms;. — Regarding the 

 classification of the Irregnlar Echinoidea I have not said a word on that subject in Part I, and ac- 

 cordingly I ha\ e not condemned it either in passing or in a more thorough way. I have only sng- 

 gested that there would pro\e to be some uncertainty in the determinations of these foi^ms, made vvith- 



nt the nse of the microscopic characters afforded by pedicellariæ etc. That I was quite right in that 

 suggestion is, I thiuk, sufficientl\ pro\ed in this second Part of my work. 



To turn now to the cases among the Cidarida' pointed out b\ Professor Agassiz as especialh' 

 nnfortnnate results of ni\- classificator> attempts. Such a case is the uniting of Cidaris mctularia and 

 verticillata in one genus — two species which are more readily distinguished b\- the characters of the 

 spines and tests than an\ other species of the family . That Cidaris baculosa is added to the same 

 genus is also held very unfortunate. It is true that Cidaris verticillata and metularia are \ery readil\ 

 distinguished by their spines as well as by their tests; the differences found in the spines, however, 

 could not convince me of the absnrdit\ of uniting them in one genus, since I was unabie to see very 

 reliable generic characters in the structures of the spines — and certainly the differences between the 

 spines of C. verticillata and imitilaria are not more importaiit than are those between C. verticillata and 

 Fhyllacanthiis imperialis. which are united in one genus in the Revision of Echini . As for the differ- 

 ences in the structure of the test I might well have ascribed to them more systematic importance, if I 

 had been fortunate enough to have had a specimen of this C. verticillata at ni)- disposal and had been able 

 to make a direct comparison. (It was upon the whole the lack of sufficient material for a comparative 

 study of the tests of the Cidarids which made me unabie to judge of the real value of these structures 

 for the distinctiou of the genera.) Being then constrained to class the species after the structure of the 

 pedicellariæ I could not get an> other result than that these two species had ,to be regarded as not 

 too closely allied .species of the same genus (p. 15), and since Professor Doderlein (Op. cit. p. loi) 

 after his ver\ elaborate studies on the tests, the pedicellariæ and spines of the Cidarids has now corae 

 to the result that C. vertillata. baculosa and »letnlaria ha\e to be placed in the same genus, only in 

 different subgenera, I cannot think m\- result so ver\ mmatural. 



That Cidaris affinis is separated from Darucidaris papillata. with which latter species it was 

 hitherto made sjuonymous, and even placed in another genus, Professor Agassiz finds erroneous. 



There is nothing in the fignres of the pedicellariæ given by Mortensen to w arrant such a transposi- 

 tion (p. 22). As evidence thereof the fignres of pedicellariæ of these two species given on PI. IX are 

 cited. That the fignres of the tridentate pedicellariæ as well as those of the small globiferous pedicel- 

 lariæ do not show so very important differences I willingh' agree, but I ha\e not used these differences 

 as distinguishing characters of the genera Dorocidaris and Cidaris. The main difference between 

 the two genera I find in the large globiferous ])edicellariæ; of the figures given thereof Profes.sor 



