248 MR. W. PERCY SLADEN ON THE 



tt One marginal spine. Ambulacral spines 4 or 5 in 

 the inner series ; outer part of plate occupied by a 

 group of papilliform and equal-sized spinelets. . . . brevispinus. 



B. With one series of definite spines on the supero-mar- 



ginal plates. 

 t With lai-ge, prominent spines on the supero-mar- 

 ginal plates. 



* With large well-developed spines on the infero- 



margiual plates. No naked spaces poly acanthus. 



tt With small spines on the supero-marginal plates. 



* The series of supero-marginal spines continuous 



throughout the ray. 



1. Marginal spines 4 in an oblique comb. Ambu- 



lacral spines in 3 series, 3 in each pectinatus. 



2. Marginal spine 1, long and cylindrical, with 2 



small companions close behind. Ambulacral 

 spines of the second and third rows frequently 

 grouped, normally 3 in each. A spine on the 

 infero-marginal plate near the adambulacral 



plates acanthifer. 



** The series of supero-marginal spines not continuous 

 throughout the ray. 

 II Wanting in the interbrachial angle. 

 0. Marginal spine 1. Ambulacral spines in 3 



series japonicus. 



II II Wanting on the outer half of the ray, but 

 continuous in the interbrachial angle. 



0. Marginal spines 3. Ambulacral spines in 



2 series imbellis, 



C. With only an indefinite spinelet, or several enlarged 



granules on the supero-marginal plates. 

 t With 3 ambulacral spines in the second series. 



* Marginal spine I. Outer ambulacral spines very 



broad and flaring. No aboral line of spinelets. 



on the infero-marginal plates hermatophilus. 



** Marginal spines 4 or 5 in diagonal line. Outer am- 

 bulacral spines short, not broad or flaring, placed 

 diagonally. An aboral line of spinelets on the 

 infero-marginal plates pontoporceus. 



D. With no spinelets on the supero-marginal plates ; ex- 



cepting in some species a very small one on the first 

 or first 4 or 5 in the arm-angle, 

 t With small spinelets on the first 4 or 5 plates. 



* With 4 or 5 spinelets. A well-developed series of 



pseudo-pedicellarise zebra. 



** With 1 spine only, on first plate. No pedicel- 



larise velitaris. 



tt With no spines whatever on the supero-marginal 

 plates. 



* Marginal spines 1. 



With 2 or 3 ambulacral spines in the second series. 



1. Supero-marginal plates broad, with small 



granules. Paxillse with 5-8 granules (or 



spinelets) on the central tabulum granulatus. 



2. Supero-marginal plates narrow, with large 



granules. Paxillse with one granule on 



the central tabulum monacanthus. 



