100 ZOROASTERIDAE. 



correct. There are no adradials. "The prominent plates immediately adjacent 

 to the carinals and overlapping them are almost certainly the superomarginals. 

 .... There are therefore on each side of the carinals 2 series of marginals and 

 5 actinolateral series. The superomarginals are alternately larger and smaller." 



Zoroaster. 



Wtville Thomson, 1873. Depths of the Sea, p. 154. 

 Type-species: Z. Jidgens Wtville Thomson, 1873. Loc. cif. 



Even as here restricted, this genus contains twenty-two species, and two 

 subspecies. It is no easy matter to separate them from each other, for the 

 specific characters are not numerous and several are very ill-defined, so that 

 even when species look as unUke as fulgens and longicaudus it is not easy to 

 express their differences briefly with reliable accm-acy. So httle is known of 

 growth-changes in the genus, it is quite likely the key given below will prove of 

 little use with young specimens. The condition of the adradial series of plates 

 furnishes the most important divisional character as it usually shows relatively 

 Uttle growth-change, and yet in ackleyi at least, it is well-marked in specimens 

 with R = 50 mm. and quite concealed when R = 100 mm. The character and 

 degree of armature of the carinal and superomarginal plates furnish good but 

 less reliable features, and the tuberculation and spinulation of the actinolateral 

 plates are of some service. But the relative length of arm increases more or 

 less considerably with age and consequently body-form and proportions are not 

 rehable, while the armature of the adambulacral and oral plates shows relatively 

 Uttle diversity in the genus. Nevertheless specific hnes can be drawn with more 

 or less accuracy and the following key will help to differentiate the species. It 

 includes the new species described below, as well as the subspecies named by 

 Fisher. 



Key to the species of Zoroaster. 



A. Adradial series of plates well-developed at least on basal half of ray. 

 B. Superomarginals, some or all, armed with a central spine. 



C. Most skeletal plates, except some or all adradials, with a stout central spine. 



D. Abactinal plates nearly or quite without spinelets perarmaius. 



DD. Abactinal plates well-covered with spinelets. 



E. No large pediceUaria regularly on second spine of projecting adambulacral plates. 



evermanni. 

 EE. A huge pediceUaria on second spine of each projecting adambulacral plate. 



evermanni mordax. 

 CC. Most skeletal plates without a central spine. 



D.' Carinal plates wider than long; superomarginal spines irregiilarly developed, often wanting 

 on most of the plates. 



