PRIONECHINUS. 303 



species, as any other course would result in great confusion; and this decision 

 is strengthened by the fact that the specimens collected by the "Siboga" and 

 determined by de Meijere as sagittiger seem to be identical with it. This state- 

 ment is made from the study of a specimen from the "Siboga" material now in 

 the M. C. Z. collection. Mortensen states that the specimen from "Challenger" 

 Station 207 is not a Prionechinus, "it is, no doubt, a quite different genus." 

 As he gives no facts in support of this blunt assertion, except that "the pores 

 are really very large and form a straight line," the matter cannot be regarded 

 as settled. A reexamination of a specimen from "Challenger" Station 164 

 shows that it has ten buccal tube-feet and several large plates covering the 

 periproct, in both these respects differing from sagittiger. Apparently it was 

 from such a specimen that fig. 13, PI. VI a of the "Challenger" Report was 

 drawn and so far as can be seen such specimens belong to the species Agassizii. 

 But it is certainly very doubtful how important as a specific character the 

 absence of a tube-foot from one or more of the buccal plates, really is, and the 

 same is true of the presence or absence of several large plates in the covering 

 of the periproct. In view of the fact that when Prionechinus sagittiger was 

 described, very little indeed was known of the living members of the group now 

 called Trigonocidarinse, and that little was based on West Indian material, it 

 seems quite natural that the "Challenger" specimens from Stations 164, 207, 

 and 218 were all referred to one species, especially since in the character of the 

 spines and in their superficial appearance they are very similar. And it should 

 be borne in mind that it is not yet demonstrated that they do not belong to a 

 single species, for should Agassizii prove to be identical with sagittiger as is by 

 no means impossible, it will be difficult to determine how the specimens from the 

 three stations are to be separated. The specimens collected by the "Siboga" 

 and identified as Forbesiana by de Meijere, do not seem to belong to that species, 

 so far as can be judged from the small specimen at hand. But the agreement in 

 coloration is rather striking and the differences in tuberculation which we note 

 may be largely a question of age. Doderlein's species, Chuni, appears to be 

 very well characterized and this seems equally true of the Hawaiian species 

 sculptus. The species depressus from the Hawaiian Islands and ruber from Japan 

 are much more dubious. 



The following table will show the characters that seem to separate these 

 seven species from each other: 



Test high, vertical diameter distinctly more than one half horizontal; buccal plates 10, 

 subequal, each with a tube-foot, the 5 pairs well separated from each other; peri- 

 proct covered by numerous, nearly equal graniform plates Chuni. 



