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be found also on the proximal side of the third adambulacral spine. 



The above may be taken as the typical arrangement of the 

 armature of the adambulacral plate. In one specimen however the 

 third adambulacral spine was wanting and there were two or 

 three pedicellaria3 instead of one or two. In this specimen the 

 spines were on the whole less well developed. 



The first adambulacral plate usually bears a single series of 

 four or five spines which gradually increase in size outwards, 

 and the second bears usually one less spines of the same form 

 and arrangement. 



Mouth-plates. — The mouth-plates are narrow, very slightly 

 curved, and elongated. Each plate has two ridges, the main 

 one on the actinal surface, and a secondary one on the mouth 

 side, parallel with the ambulacral furrow. On the main ridge 

 there are some ten or a few more large spines forming a some- 

 what irrciïular series, of which one or two at or near the mouth 

 end may be conspicuously larger than the others (PI. V, fig. 

 82). These large spines are usually situated on the inner two- 

 thirds of the plate, while the outer one -third is covered with some 

 twenty or more smaller spines without any regular arrangement. 

 Near the centre of the actinal surface of the coupled plates there 

 are some six or seven spines intermediate in size between the 

 larger and the smaller ones. There are also some small spines 

 on the lateral surface of each mouth-plate. The secondary ridge 

 bears some seven to ten spines similar in form and size to 

 the smaller spines of the main ridge ; one of them at the mouth 

 end may be conspicuously larger than the rest 



Veyitrolaterals. — The ventrolateral plates are very small and 

 inconspicuous. In each interradius there are some nine or ten 



