8 INTKODUCTION. 



in all probability was developed gradually in palseontological time from 

 the disk, and that the vault of the Camerata was in its extreme form an 

 extravagantly developed or modified disk ; so that we may with them 

 consider that all the plates between the rays represent the same element, 

 whether they are large or small, heavy or thin, regularly or irregularly 

 arranged, resting upon the basals or the radials, and whether interradial 

 or perisomatic; and that the differentiations which are found among dif- 

 ferent groups are due to modifications which the Crinoids have undergone 

 palajontologically, — a view which Carpenter in his letters to Wachsmuth 

 and myself fully indorsed. 



Another interesting structural feature in Calamocrinus is the limitation 

 of the articular facet to the middle of the radial. This is an eminently 

 embryonic character, and there are traces of it in some of the forms of 

 Millericrinus described by de Loriol in his Jurassic Crinoids, — specially 

 in M. Milleri. 



Dr. P. H. Carpenter, in his Report on the Crinoidea of the Challenger 

 (p. 193), says that Leuckart, in his Jahresbericht for 1864 and 1865, di- 

 vided the Echinoderms into Pelmatozoa, Echinozoa, and Scytodermata, and 

 that, working back from this year. Professor Bell eventually succeeded in 

 tracing this classification of Leuckart's to a morphological essay published 

 in 1848, where, however, the familiar name x\ctinozoa is used to denote 

 the Urchins and Starfishes together. It is strange that Leuckart's paper 

 on the Morphologic der Wirbellosen Thieren (1848) should not have been 

 familiar to both Bell and Carpenter, for it was in that same essay that 

 Leuckart first established the division of the Coelenterata which has been 

 so universally adopted by naturalists. This is the more i-emarkable as 

 in Agassiz's "Contributions to the Natural History of the United States," 

 Vol. I. p. 208, a summary of Leuckart's classification is given in the " Es- 

 say on Classification." This Essay on Classification was also published in 

 London in 1859. 



The statement made by Carpenter, that the Jahresbericht for 1864 and 

 1865 contained a division of the Echinoderms into Pelmatozoa, Echinozoa, 

 and Scytodermata, is not correct. Leuckart speaks in that Report of the 

 Scytodermata, Echinida, Asterida, Ophiurida, and Pelmatozoa. The Echi- 

 nozoa are not mentioned ; in fact, the Echinozoa are not mentioned by 

 Leuckart at all in any of his Reports. We find in his Morphologie a first 

 Class of Echinoderms, the Pelmatozoa, with two orders, the Cystids and 



/ 

 / 



