NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 21 



4987) and caryi was taken at station 4892 while saga-minus was found 

 close by at station 4894. 



It seems clear from this unusual array of facts regarding their dis- 

 tribution that ophiurans do not as a group well illustrate " Jordan's 

 Law," which has been stated as follows: 



Given any species (or kind) in any region, the nearest related species (or kind) is 

 not to be found in the same region nor in a remote region, but in a neighboring district 

 separated from the first by a barrier of some sort or at least by a belt of country, the 

 breadth of which gives the effect of a barrier. 



Jordan adds (pp. 73, 74) : 



This law holds good as a general rule among animals. The only exceptions yet 

 indicated are found among plants * * *, among Protozoa * * * and in a 

 few cases which seem to be explainable on the ground of reinvasion. 



So far as we have any evidence there is neither "barrier" nor "belt 

 of country" separating the ophiurans mentioned above from their 

 nearest allies. Further evidence in support of this conclusion may 

 be gleaned from Lyman's reports on the ophiurans collected by the 

 Challenger and the Blake. b One illustration from each will suffice. 

 The genus Ophioplinthus contains only two known species (grisea and 

 medusa) ; they were taken by the Challenger at the same station (156), 

 in very deep water (1,975 fathoms) in the Antarctic Ocean and have 

 never been taken elsewhere. The Blake collected near Martinique 

 (station 203) in 96 fathoms of water, and near Santa Cruz (station 

 132) in 115 fathoms, a remarkably well characterized species (tuber- 

 culosa) of Hemieuryale, a genus which was previously monotypic. 

 The known species (pustulata) was, however, common at both the 

 stations where tuberculosa occurred. It may be worth mentioning 

 that Sigsbeia murrhina, whose nearest ally is probably Hemieuryale, 

 was also common at both stations. These cases from the Challenger 

 and Blake collections agree in that the two species concerned in each 

 instance are not merely congeneric and the only known species of the 

 genus, but they are very closely allied, although differing by very 

 definite characters. 



One other illustration may be given in this matter, not simply to 

 add weight to the preceding evidence, but because it affords an expla- 



a D. S. Jordan, Isolation as a Factor in Organic Evolution: in Fifty Years of Dar- 

 winism, 1909, p. 73. 



b Kcehler's great work on the Siboga ophiurans furnishes numerous similar cases, 

 but it is not necessary to detail them here. Suffice it to say that at Banda, the Siboga 

 collected eleven species of Ophiothrix, at its station 50, ten species and at station 99, 

 nine species. It also took six species of Ophiacantha (in a restricted sense) and five 

 of Ophiura at station 45, and six species of Ophiacantha were also taken at station 85. 



c Verrill (1899, Oph. Bahama Exp., in Bull. Lab. Nat. Hist. Univ. Iowa, vol. 5, p. 

 70) makes Hemieuryale tuberculosa the type of a new genus, but whether such a genus 

 is accepted or not the fact remains that the nearest ally of tuberculosa is undoubtedly 

 H. pustulata.. 



