DESCRIPTION OF PI. \TI.~ 



In the plates, the numbers designating figures air in heavy-faced italics, find m all cages they occur below the figure*. 

 usually on the left lower side. In order to see the full dct.vl of the he<heitypc photographic platen, also Plate 57, they should 

 he examined with a reading glass. In most cases only a single' page reference is given, which indicate* the page on which 

 the species is described. It is inexpedient usually to give references to the morphological or other part* of thw memoir 

 where the figures are discussed. 



When the correct axes of a specimen are known, these are indicated by the I.oven method of enumeration, the ambulacra 

 being numbered I, II, III, IV, and V, and the interambulaera 1, -. '>. I. and .">, the numbers revolving from left to right, or 

 eloekwise; when the specimen is viewed from below, Plate '_', tig I ; when viewed from alxivc, the numbers revolve counter- 

 clockwise, Plate' I", IIL 



When the correct axes of a specimen are not known, as m mo.-t Palaeozoic Kchim, the areas arc lettered arbitrarily A, 

 B, C. D, K, F, <!, II. I, and J, the ambulacra being lettered I!. I). I. II. and .1. The lettering revolves from left to right 

 when the specimen is viewed from above, and in external view, Plate 1 1. !ig. '.'; when viewed from below, the numbers revolve 

 counter-clockwise, Plate 11, fig. 1 (p. 20). 



It is important to bear in mind that when a specimen is viewed from the interior :an external mold i neceasarily in 

 internal view), the oriental ion and the lettering of ambulacra! and intcramhulaeral columns of plated are reversed from that 

 seen from the exterior (p. 20), Plate 23. figs. 1 and 3 (compare Plate .V.. figs. 1 and '.'.. 



In the test as n whole, the lettering is as follows: n. t>. the left and right columns of ambulacra! plates in an area, Plate 

 31, fig. 1; or n. a'; b', b, the two columns of demi-plates, <i. l>. and the two columns of occluded plates, a', 6', when there are 

 four or more columns of ambulacra! plates in an area. Plate I.', tig. '_'; Plate .Ml. fig. I 



The interambtilacral columns in an area are numbered from 1 upward as they appear pawing aborally in a given area, 

 Plate '_'(>; Plate 45, fig. 1. H, the heiila.uonal plate, associated with the initial |x-ntagnnal plate of a new column as intro- 

 duced, is seen in many I'alaeo/.oie Kchim. Plate !">. fig. 1; ;/. genital plate; <><.. ocular plate; and sr.. suranal plate. Plate- t. 

 figs. 1, 2, and 7. The letter \ has no ele'finite> meaning, but is nse-el to call attention tei s|M'e'itie- parts. Plate 2.">. figs. 1 and-. 



Lettering e>f the> parts e>f the' Aristotle's lantern with the' associated muscles is as follows: /,. brace; c, compass; 



dental capsules; eon., condylen of brace; rr., crests of the epiphyw*, when net) are <li'vclo|>cd; > >>.. external brai-e muscles; 



<'IL, e'piphyses; fit. r., anel/o. i., external and internal foramina in the> brace for articulation with the tulx-reles of the epip 1 

 <ll., gle'iioiel cavity of an epiphysis, which rece'ive's the eondyle of the brace: i. intereompa.-* n.uscles; t. 6., internal brace 

 muscles; ///..inlet-pyramidal muscles; /. /., left half of a pyramiel; /.. protract e>r muscles of the lantern; />. .x., pyramidal 

 suture that divides the' left anil right half of a single pyramid; r, radial ceimpas- muscle*; n .. retrae-tor muscles of the lantern; 

 r. p., right half of a pyramid; *. suture', applied te> different parts; .x. </.. dental slide that supports the t<x>th; xl.. styloid 

 processes which are the dorsal extension of the elental slides in eertain Kehini; I, t<Mith; In. < . and l.t. i.. external ami intenial 

 tubercles of the' e'piphyse's which interlock with corresponding foramina of the' braces, Plate' '2. figs. 7-17, and 19-21 ; P. 

 figs. 1-12. 



