108 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



ossicles beyond the second axillaries; they lie side by side in the median line of the 

 figure, the correspondmg pinnules on the outer side of the ray are more or less 

 concealed ]>y the Pi>), the use of these infonor capitals serving to differentiate these 

 puuuiles from those of the inner side of the arm. 



DESCRIPTION OF A COMATULID. 



Before takuig uj) the detailed description of the mdividual structures which 

 collectively make up the comatulid whole, it would be well to give a short sketch of 

 the more important features of the comatulid organization in their logical sequence, 

 in order that these structures may jjroperly be appreciated as uitegral parts of a 

 collective entity. It has been a common fault in works of monographic scope to 

 discuss each structure in great detail without giving a description of the entire animal 

 as the sum of its component structures, so that, imless the reader is himself possessed 

 of a veiy considerable knowledge of the subject, he is often quite unable, without an 

 enormous amount of study, to appraise each feature of the animal in its true pro- 

 j)ortion. It is hoped that the following short sketch will servo to present a con- 

 nected picture of a comatulid whereby the detailed account of each separate structure 

 will be made more easy of comprehension. 



For purj)oses of systematic description a comatulid (fig. 1, j). 60) is discussed 

 under eight distinct subheadmgs, viz: 



(1) The Centrodorsal, 



(2) The Cirri, 



(3) The Basal rays, 



(4) The Radials, 



(5) The Division series, 



(6) The Free undivided arms, 



(7) The Disk and Ambulacra, and 



(8) The Pinnules. 



This has, after many trials, been found to be the most satisfactory method 

 of treatment from a systematic pouit of view. 



(1) The Centrodorsal (see figs. 1, p. 60, 14, p. 65, and 29, 30, p. 71) is the 

 stellate, discoidal, button-like, conical or columnar central or apical j)late, from 

 which all the other structures ap{)oar to radiate; it is situated in the exact center 

 of the aboral (dorsal) side of the animal. 



The centrodorsal bears on its sides more or less numerous shallow pits or facets, 

 each ^\^th a small central ])erforation, known as Cirrus sockets or Cirrus facets (see 

 figs. 94, p. 155, and 96-98, p. 159), which mark the place of attachment of the Cirri (see 

 figs. 101, 102, p. 163, and 105, p. 169). These cirrus sockets may be arranged m defi- 

 nite alternating horizontal rows (see figs. 174, p. 231, and 219, p. 243), or in 5 (see fig. 

 207, p. 239), 10 (see figs. 190, p. 235, 192, 194, 196, p. 237, 203, 204, p. 239, 215, 216, 

 p. 241, and 227, p. 245), 15 (see figs. 198, p. 237, 200, p. 239, and 210-214, p. 241), or 

 20 (see figs. 208, 209, p. 241) definite vertical columns, or may be closely crowded 

 and quite without any dcfmite arrangement (see figs. 172, p. 231, and 226, p. 243). 



In the fully g^o^vn of certain species belonging to the family Comasteridse tlie 

 centrodorsal may be reduced to a small thin pentagonal or stellate plate sunk to. 



