460 s. fiOTo : 



are in general similar in form to those of the middle row but 

 shorter, and separated from the latter by a spacious groove. 

 There are either two or three of these spines on a single plate ; 

 they may be equal or very different in size and shape, and are 

 generally more irregular in this respect than the spines of the 

 middle row. 



At the adcentral end of each adambulacral plate, between the 

 first and second row of spines, there are one to three forcipiform 

 pedieellariœ. They are frequently more or less curved, and when 

 there is only one it is quite large, being about half as long as 

 the well developed spines of the middle row ; but when there are 

 as many as three of them they are usually much smaller, although 

 occasionally there may be three pedicellarias on one plate, all nearly 

 as large as when there is one. The space between the middle 

 and the outermost row of adambulacral spines is usually destitute 

 of pedicellariœ, but occasionally there may be some, and in such 

 a case their position does not appear to be constant. They are 

 of the same form as those previously described, but their size is 

 variable. 



Mouth'iüates. — The moutli-plates themselves can not be seen 

 from the surface, but the spines are very conspicuous, and are 

 arranged in two rows. In the inner row there are four thick, 

 prismatic spines with blunt end at the mouth end, and four much 

 smaller and shorter ones at the other, making eight in all. The 

 surface of the! rounded ends of the thick spines is irregularly 

 grooved, somewhat like the irregular markings of some old heart- 

 wood (PI. XV, fig. 239). The spine at the mouth end has always 

 more or less the form of a triangular prism, and the rest more 

 or less that of a rectangular prism. The outer row is present 



