650 s. fioTo : 



roughly parallel with the ambulaci-al inri-ow, of ^^-hich the one or 

 two next the inoutli are particularly stouter. The two rows of 

 spines of the mouth-plates are separated 1)\' quite a distinct space. 



Ventrolaterals. — The ventrolateral plates are arranged regular- 

 ly in A'- shaped rows parallel to the ambulacral furrows, except at 

 the interradial lines near the margin of the disk, where they be- 

 come more or less irregular and verv small. ]>v far the larger number 

 of these plates bear two spines wliicli are comparatively stout and 

 blunt, l)ut there are also quite a mmiber of them with three spines, 

 and only occasionally there may be four spines on one plate. Where 

 there are three spines on one plate, they are arranged in a row, but 

 when there are four, they appear to have no regular arrangement. 

 The spines of each plate are separated from those of the neigh- 

 bouring plates by distinct spaces. The ventrolateral spines rc- 

 gularlv decrease in size awav from the ambulacral furrows. 



Ahactinal plates. — The general appearance of the abactinal 

 surface has been described above. The arrangement of the dorsal 

 plates appear to be destitute of regularity along the ridge of the 

 arms, where the plates are also of various sizes. The larger plates 

 project more prominently than the others and give rise to the 

 rough appearance mentioned above. The number and position of 

 these larger plates are very variable, but a general idea can be 

 obtained from the photographic picture reproduced in fig. 279, PL 

 XIX. On the sides of the arms there are 4-G longitudinal rows 

 of small plates, all looking similar to one another and different 

 from those of the abactinal ridge, nmning parallel to the long 

 axis of the arms and forming acutem angles with the superomargin- 

 al series. The number of spines on tliese plates may vary from 

 4 to 7. The more prominent plates near the dorsal ridge may 



