Ecliinological Notes 
by 
Dr. Th. Mortensen. 
III. The central (sur-anal) plate of the Echinoidea. 
In a series of most interesting papers 1 ) Dr. A. H. Clark 
has recently treated different points in the natural history of the 
Crinoidea in a very suggestive and ingenious manner, throwing 
new and important light on many questions in the physiology, 
phvlogeny and morphology of Crinoids. 
Among the conclusions arrived at by Dr. Clark one of the 
most startling is that of the near relationship between Crinoids 
and Echinoids. Though I am here decidedly in opposition to my 
excellent friend, as I have repeatedly emphasized in letters to 
him, it was not my intention to enter on a literary discussion of 
this matter, as a refutation of the reasons on which Dr. Clark 
has founded this conclusion would necessitate a thorough treatment 
of nearly the whole of the comparative morphology of the Echino- 
derms; but for such a work, most interesting though it would be, 
b The homologies of the arm joints and arm divisions in the recent 
Crinoids of the families of the Comatulida and the Pentacrinitidæ. 
Proc. U. S. Nat. Mus. 35. 1908. — The non-muscular articulations of 
Crinoids. American Naturalist. 43. Oct. 1909. — The affinities of 
the Echinoidea. Americ. Natural. 43. Nov. 1909. — On the Origin 
of the Crinoidal muscular articulations. Amer. Journ. Sc. 29. 1910. 
— The probable origin of the Crinoidal nervous system. Amer. Na¬ 
turak 44. Apr. 1910. — Remarks on the pentamerous symmetry of 
the Crinoidea. Amer. Journ. Sc. 29. Apr. 1910. — The phylogenetic 
interrelationships of the recent Crinoids. Proc. U. S. Nat. Mus. 38. 
May 1910. — On the Origin of certain types of Crinoid stems. Proc. 
U. S. Nat. Mus. 38. June. 1910. 
