A MONOGRAPH OF THE EXISTING CRINOIDS 



By AUSTIN HOBART CLARK 



INTRODUCTION 



THE present part, Part 4a, of Volume 1, Bulletin 82, is a continuation of Part 3 

 preceding. Part 3 contained the account of the superfamily Comasterida, and the 

 present part includes the account of the second of the three superfamilies of the 

 Oligophreata, the Mariametrida, with the exception of the family Colobometridae. 



The arrangement of the families and higher groups adopted in the present work 

 is given in Part 3, p. 65. 



Keys to the families into which the superfamily Mariametrida is divided are 

 included in the keys to the families and higher groups of the comatulids given in 

 Part 3, pp. 69-74. 



Since the portion of this monograph dealing with the structure and morphology 

 of the comatulids was published a large amount of additional work has been done by 

 others, particularly by Prof. Torsten Gislen, of the University of Lund, Sweden, 

 and many interesting and important new facts have been brought to light. 



Some of the interpretations of the structural peculiarities of the comatulids 

 advanced by these authors differ more or less widely from those given earlier in this 

 work. Though thoroughly appreciative of the vast amount of original work upon 

 which these interpretations are based, I fail to find, upon careful analysis, any reasons 

 for altering my opinions already expressed. 



The main point of divergence between my opinions and those of my colleagues 

 hinges upon the weight to be given the Paleozoic and earlier Mesozoic forms in an 

 elucidation of the structure of recent types. I maintain that until the recent crinoids 

 are far better known than they are at present, especially in regard to their younger 

 stages, it is futile to attempt to interpret the details of their structure from compari- 

 son with earlier forms. For most of the earlier forms, as we know them, represent 

 the terminal twigs of developmental branches of which the generalized beginnings 

 are unknown, just as the adults of the recent forms represent the ultimate product of 

 an unknown ontogeny. And even if the earlier stages of all the recent forms were 

 known, it is by no means certain that these would give any definite clue to their ances- 

 try and morphological relationships when compared with the adults of earlier types. 



In my opinion the most valid and logical conclusions regarding the comparative 

 structure and morphology of the recent crinoids are to be reached by detailed and 

 intensive study of the recent types alone. Until we are in possession of sufficient 

 facts to enable us to understand the recent types, and thus to be sure of our ground, 



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