£71 
6. The Classification of the Regular Echini. 
By Hubert Lyman Clark. 
(Museum of comparative Zoölogy, Cambridge, Mass., U.S.A.) 
eingeg. 9. August 1914. 
In his recently published report on the echini of southwestern 
Australia (Die Fauna Siidwest-Australiens, Ergebnisse der 
Hamburger südwest-australischen Forschungsreise 1905, 
Bd. 1V, Lf. 12. Jena 1914), Dr. Döderlein takes occasion to discuss the 
classification of the Recent regular echini, maintaining the correctness 
of Mortensen’s grouping, based upon the pedicellariae, and rejecting 
Jackson’s! arrangement of the families of Centrechinoida, which he 
calls the “alten Agassiz-Gregory’schen System”. While it is true 
that Jackson’s classification is similar to that used by Alexander 
Agassiz as modified by Gregory, it may be mentioned in passing, 
that this arrangement has so many original features and is based on 
such different morphological conceptions, it ought in all fariness to be 
called the “Jacksonian system”. 
Dr. Doderlein takes occasion to criticize in a most courteous and 
friendly spirit, the reasons which Jackson, and which I, have given for 
rejecting Mortensen’s arrangement, and yet he does not even mention 
what we consider, and what we have stated, to be the fundamental 
reasons for our course. Indeed, neither Doderlein, nor Mortensen 
himself, seems to have ever grasped the points we have endeavoured to 
bring out and it therefore seems not only desirable but necessary to 
emphasize these points in a brief and isolated statement, such as.this 
note. At present Continental zodlogists seem inclined to follow Mor- 
tensen, while those of England and America follow Jackson, and 
this suggests the possibility that Jackson’s arguments are not clearly 
understood on the Continent. 
The disagreements between Mortensen’s and Jackson’s classi- 
fication of the Centrechinoida arise from the fact that the characters of 
the test and those of the appendages of the test (spines, pedicellariae 
and spicules in the tube-feet) are not perfectly correlated. Mortensen 
follows the guidance of the appendages (particularly the pedicellariae 
and the spicules) while Jackson adheres to the characteristics of the 
test. Jackson’s first argument is that the test is more fundamental 
-than any of its appendages and therefore it shows more deeply seated 
1 Phylogeny of the Echini, with a Revision of Palaeozoic species by Robert 
Tracy Jackson. Mem. Boston Soc. Nat. Hist., vol. 7, 1912. 
