Terms in Crinoid Morphology, .53 



Bracliiah — ^ arm-ossicles, or, in otlier words, all ossicles 

 situated in the direction of the rays, distal to tlie 

 radial (.<?. str.) and belonging to the abactinal system. 



Costah = \\\^ first order of brachials, i. e. all brachials from 

 the radial up to and including the first axillary. 



Dis(iclials = t\\c second order of brachials. 



Pabnars = ihc third order of brachials. 



First PosfpaItnai's = i\ie fourth order of brachials. 



Second PostpaJmars=.i\\c fifth order of brachials ; and so on. 



Free Brachials = a.\\ brachials after the last axillary, which- 

 ever that axillary may be. 



Through the kindness of Dr. Carpenter I had already been 

 able to put forward the above terminology * and to announce 

 that it would be used in my papers on British Fossil Grinoids. 

 Waclismuth and iSpringer had also privately expressed their 

 intention of accepting it. The latter authors, however, have 

 already found it necessary to modify it slightly f. " To the 

 most of this terminology," they say, " we entirely agreed, but 

 in some particulars it does not quite meet the requirement in 

 dealing with the greater complexity and variety of construc- 

 tion found in the Palaeozoic forms." Instead of applying the 

 term Free Brachials to brachials after tiie last axillary only, 

 they use it in a different and extended sense, applying it to 

 all brachials that are free from the calyx, as are all the arm- 

 ossicles in the Inadunata. The term is thus opposed to Fixed 

 Brachials, by which is meant those arm-ossicles incorporated 

 in the calyx, such as are often found in the Camerata. 



In the same place Wachsmutii and Springer have supple- 

 mented the above terminology, as follows : — 



^^Tnferradials, all plates interradially disposed in the calyx. 

 ^^Interbi-achials, a general term for all plates between the rays 



above the radials. 

 " Intei-distichals, the plates between the first divisions of the 



ray. 

 "Interpahiiars, those between the second divisions of the ray. 

 " Interambulacralsj the plates between the ambulacra." 



In applying to Palaeozoic Crinoids the terminology to which 

 I stood committed, I soon stumbled on certain difficulties. 

 This was especially the case in the attempt to work, out and 



* " Brit. Foss. Criu., II.,'' Ann. & Mag. Nat. Hist. (6) vol. v. p. 313, 

 April 1890. 



t "The Perisomic Plates of tlie Crinoids," Proc. Acad. Nat. Sci. 

 Philadelphia, vol. for 1890, p. 374 : Feb. 1891. 



