﻿2 INTRODUCTION. 



fore, all measurements in these descriptions may be directly compared 

 with each other, and proportions, or tables, may be made from them. 

 All the species are described in the same way, and ui accordance 

 with the following table : — 



1. Names. 



2. Principal Stnoxymes, with references to their authorities. These have been taken 



from the original works, whenever it was possible. 



3. Special Marks. A few striking charactere are given, to aid the student in finding 



a particular species. 



4. Description of a Specimen.^ A specimen is particularly described, as an indi- 



vidual, and without reference to other individuals. Its parts are taken up in 

 the following order : — 



a. General measurements. Diameter of the disk. Distance from the outer edge of 



a mouth-shield^ (Fig 9, a) to the outer corner of the opposite mouth-slit.' 

 Width of an arm, without its spines. Length of an arm. Distance from the 

 outer side of a mouth-shield to the inner point of the corresponding angle of 

 the mouth (Fig. 15, c), compared with the distance between the outer corners 

 of two mouth-slits. 



b. Chewing apparatus. Number, shape, size, &c. of the mouth-papilltB (Fig. 15, d) ; 



tooth-papilla; < (Fig. 5, d') ; and teeth* (Fig. 5, d"). 



c. 3Iouth-shields, their shape, and length to breadth; peculiarities of the madre- 



poric shield. 



d. Side mouth-shields'^ (Fig- 9j *)> tlieir size and shape. 



e. Under arm-plates^ (Fig. .3, ^), their shape, size, and proportions. These plates 



are often octagonal, in which case the two sides that are parallel with the 

 length of the arm are called lateral (Fig. 11, h"") ; the two that run across the 

 arm, outer (Fig. 11, h") and inner ; and the four sides that stand at an angle 

 with the length of the arm, respectively outer lateral and i7iner lateral 

 (Fig. 11, h' and h'"). In counting the joints, or the plates, of the arm, the 

 innermost under arm-plate (which is often quite rudimentary) is considered as 

 the first. 



f. Side arm-plates^ (Fig. 3, i), their form and character. 



g. Upper arm-plates'^ (Fig. 2, _;'), their shape, size, and proportions. Their dif- 



ferent sides are named in the same way as those of the under arm-plates. In 

 some genera these plates have supplementaiij pieces, which are always placed 

 near the edges, but vary in number, size, and shape. 

 h. Disk, details of its covering, above and below. Tlie disk is divided into bra- 

 chial and inlerhrachial spaces, the former including the sectois, which contain 

 the arms, the latter those which are between the arms. When the scaly coat 

 is not entirely covered by grains, or spines, there may be distinguished certain 



' For a short anatomical description, see Lutken on Ophiurans, Silliman's Journal, XXVIII. 

 July, 1859. 



°- Mundschild (Mull.) Scutum buccals (Mull.). 



" Mundspalten (Miill.) Rima oris. 



* Zahnpapillon (:Mu11.) Papillae deutales. 



^ Zahne (Miill.) Dontes. 



° Scutella adoralia. 



' Bauclischilder (Miill.) Scutella ventralia. 



' Scutella lateralia. 



' Riickenschilder (Miill.) Scutella dorsaha. 



