184 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Phylogeuotic facts must be acquired throu{i;h the study of the comparative 

 anatomy of the group, combined witli the study of the embryology and later 

 development; later they may be tested in the light of the palirontological record 

 if one so desires. 



In every group of animals we must be very careful how we apply the data 

 gain<>d from the ])aIs6ontological record, and in no group is this care more necessary 

 than in the crinoids. 



The earliest crinoids present many characters which are highly speciaUzcd, 

 and in general this specialization is al(»ng quite different lines from the specialization 

 in recent forms. Upon careful analysis they reduce themselves to a basic typo 

 characterized bv (1) a urdform cylindrical column of continuous growth; (2) a very 

 large calvx with an enlarged and asjnnmetrical anal area, including one or more 

 extra plates, and with a subradial plate beneath the right posterior radial; and 

 (3) short biserial arms. The post-palseozoic crinoids, excepting the Encrinidaj, upon 

 careful analysis reduce themselves to a basic type characterized by (1) a column 

 possessuig a defmite limit of growth and terminated proximally by a specialized 

 columnal with more or less of the character of a calyx plate; (2) a greatly reduced 

 and ])erfectly symmetrical calyx with no additional plates in the anal area and no 

 subradials; and (3) very long uniserial arms. In all throo of these characters the 

 earlier crinoids are much more primitive than the later. 



The phylogenetic history of the crinoids, in agreement with the palaeontological 

 record and with the ontogeny, indicates that there has been a progressive and 

 rapid decrease in the size of the visceral mass, correlated with a proportionate 

 increase in the size and length of the arms. This reduction in the size of the vis- 

 ceral mass, and of the calyx plates, resulted in the eventual elimmation from the 

 caljTC of the subradials and of the interradials, leaving it composed only of the 

 infrabasals, basals and radials, wliile in the phylogenetically most advanced tj'pes 

 even the infrabasals, and in some extreme cases the basals also, have become meta- 

 morphosed or disappeared, so that the calyx is composed of radials only. 



We can not reconstruct the ancestral crinoid type from what we actually find 

 in the palaeozoic rocks, for every palaeozoic form is specialized in at least a minority 

 of its characters. For instance, in certain forms, in other ways possessing a com- 

 paratively liigh degree of specialization, the visceral mass has retained more or less 

 its j)rimitive large size, so that we fuul the radianal (the right posterior subradial) 

 repeated under one or more, sometinaes under all, of the other radials, as in For- 

 hesiocrinua; while among the jjalaeozoic forms the majoritj' possess a very primitive 

 type of column though there are several noteworthy exceptions, as for instance, 

 Platycrinus (fig. 516, pi. 1); many possess the primitive biserial type of arm, and a 

 few possess a \cvy primitive type of calyx usually, however, combined with a 

 specialized tj^ie of arm. 



We must therefore reach our conclusions by a careful process of deduction, 

 and the result, arrived at through a critical study of the data presented by the 

 palaeozoic and later species, and especially by a study of th(> development and 

 morphology of the recent types, gives us an organism which, though closely ap- 



