A MONOGRAPH OF THE EXISTING CRINOIDS. 



By AUSTIN HOBART CLARK, 



Curator. Division of Echinoderins, United States National Museum. 



STRUCTURE AND ANATOMY. 



RAIIIAI.S : Continued. 



[Fart 2 of volume 1, Bulletin 82, is a direct continuation of part 1 published 

 in 1915, taking up the discussion of the structure and anatomy of the unstalked 

 crinoids at the point at which it was left in 1915. In this part the introductory 

 matter is concluded. 



For assistance in the preparation of the following pages I am especially indebted 

 to Dr. Hubert Lyman Clark, who had the kindness to read through the entire 

 manuscript; to Prof. William Morton Wheeler, who was so good as to examine 

 for me the section dealing with parasites and commensals; to Prof. Charles 

 Branch Wilson, who revised my list of parasitic copepods; to Mr. William F. 

 Clapp, who revised my account of the parasitic Mollusca; and to Dr. Henry A. 

 Pilsbry, to whom I submitted my list of commensal barnacles. Mr. Frank 

 Springer has, as before, kept constantly in touch with the work as it progressed, 

 and I am deeply indebted to him for a very large number of most helpful sug- 

 gestions indeed, whatever merit there may be .in those portions dealing with 

 crinoidal morphology is very largely the result of his advice and inspiration. I 

 am also under obligations to Dr. Herrick E. Wilson for his kindness in reading 

 the greater part of the manuscript, as well as for numerous suggestions.] 



Articular Faces of the Radials. 



No detailed comparative study of the sculpture of the articular faces of 

 the radials has as yet been attempted; in fact, only three authors have even so 

 much as mentioned them. W. B. Carpenter in 1866 described minutely the con- 

 ditions found in Antedon bifida; P. H. Carpenter in 1888 figured and described 

 them in such species (distributed among several families) as he was able to 

 dissect; and C. Hartlaub in 1895 and in 1912 published some additional facts 

 concerning them based upon his study of various species from Panama, the 

 Galapagos Islands, and the West Indies. 



Yet a detailed and accurate comprehension of the characters of the articular 

 faces of the radials is essential in the study of the comatulids as a whole, for 

 in very many cases the fossil species are represented only by specimens consist- 

 ing of the centrodorsal and the radial pentagon, and without a true conception 

 of the fundamental and diagnostic features involved, and of the limits of vari- 



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