^8 t ' Mr. F. A. V.athcr—f^ufj jested 



This system lias the advantage of at once conveying to the 

 ipind, in the simplest possible manner, tlie desired ideas. It is 

 obviou'sly capable of indefinite extension ; but, since very few- 

 arms branch as many as twelve times, it does not involve 

 wor(3s of any great length. It is true that " primibrachs " 

 is longer than " costals ; " but then " the fourth sextibrach " 

 is far shorter than '' the fourth brachial of the third post- 

 palmar series " or even than '^ the fourth ossicle after the fifth 

 axillary," which latter is a perijihrasis proposed to me by 

 Mr. Wachsmuth. Besides, the system is merely a more con- 

 venient rendering of terms that have been, and are still, 

 employed by authors of repute, including Wachsmuth and 

 Springer. In a letter dated August 5th, 1891, Mr. Wachs- 

 muth writes : " The terminology of the brachials which you 

 propose is almost the same which' I proposed to CaTpenter 

 wdien we discussed the question two years ago, with the 

 exception that I called the costals ' primary brachials,' the 

 distichals * secondary brachials.' At first we thought these 

 terms wel-e excellent, but, using them in some of our descrip- 

 tions, we found them extremely cumbrous, and this induced 

 us to accept Carpenter's terms." He adds, however, " w^e 

 occasionally use primary and secondary brachials in place of 

 costals and distichals as a change." The alteration involved 

 in adopting the proposed system is therefore of the smallest 

 possible kind, while the terms have all the ' excellence ' 

 without the * cumbrousness ' of those still used occasionally 

 by Wachsmuth and Springer. 



A still greater advantage of the new system is that it can 

 be extended to all parallel structures. The general term at 

 present applied to the covering-plates of the ventral grooves 

 is " ambulacralia." This word may be conveniently short- 

 ened in composition, and the various series denoted as " prini- 

 nmbulacs " &c. A similar nomenclature can be applied to 

 cirrus-ossicles or " cirrals," and to root-ossicles or " radicals," 

 in cases where these branch. 



The supplementary plates that occur in some Camerata 

 between the secundibrachs and tcrtiobrachs of a single ray 

 have been called " Interdistichals " and " Interpalmars." 

 The change to " Intersecundibrachs " and " Intertertiobrachs " 

 is hardly euphonious; but there is rarely occasion to use these 

 terms. The corresponding plates of the ventral surface should 

 of course be known as " Intersccuntlambulacs " and " Inter- 

 tertambulacs : " these plates have hitherto had no distinctive 

 names, and some may think that it was better so. 



As yet wc have only considered the proposed system in its 

 application to simple or non-pinnulate arms, when those are 



