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on the external side, they are covered with capillary spinelets 

 similar to those of the snperomarginals. 



Adamhulacral plates. — These are much broader than long for 

 the greater part of the arm, and very much inclined to the furrow 

 at the base of the arm (PI. Ill, fig. 36, 38). About the middle 

 of the arm there are 5 of these plates to every 3 of the infero- 

 marginals. The adamhulacral spines on one of the proximal plates 

 are as follows : one spine longer than the others at the apex 

 of each plate, then one pair, then a second pair, then a third 

 pair or three in a row, and a few smaller spines. In a more 

 distal plate the first five (one apical and two pairs) are usually 

 present, but the rest are subject to variation. The relative size 

 of the first pair mentioned by Dödeklein is frequently, but not 

 always, true ; the proximal and distal spines are often of the same 

 length, or the former may even be longer. These spines are more 

 or less flattened, and have rounded apices. 



Mouth-plates. — These are very prominent in specimens from 

 which the actinal spines have been removed ; they are narrow, 

 slightly curved, and ankylosed with each other at the two ends, 

 leaving a small space between covered over with a membrane 

 (PI. Ill, fig. 36). Each plate has a main crest and an accessory 

 ridge, the former extending through the whole length of the plate, 

 the latter about one-third as long, and situated on the furrow 

 side of the mouth end, lying in fact in a line with the furrow 

 margins of the adamhulacral plates (PL III, fig. 36, 37). The 

 main crest bears about 10 short, robust, conical spines ; and the 

 accessory ridge bears 4-5 smaller spines, of which the most 

 proximal (next the mouth) is of nearly equal size with those of 

 the main crest. A few distal spines of the main crest are more 



